3B Scientific Air Cushion Plate User Manual

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PHYSICAL EXPERIMENTS
ON THE
AIR-CUSHION TABLE
U15420
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Physical Experiments on the Air-Cushion Table
Table of Contents
Introduction ........................................................................................................................ 5
1.1 Components of the experimenting apparatus ......................................................................... 6
1.2 Principle Uses of the Air-Cushion Table ............................................................................. 11
1.3 Setup of the Air-Cushion Table ............................................................................................ 11
1.4 Instructions for Usage .......................................................................................................... 12
1.5 Maintenance and Care .......................................................................................................... 13
2 Description of the Experiments ........................................................................................ 14
2.1 Structure and Properties of Gases ...................................................................................... 14
2.1.1 Motion of a Molecule in High Vacuum ............................................................................... 14
2.1.2 Motion of the Molecules in a Gas ........................................................................................ 14
2.1.3 Dependence of the Number of Impacts with the Vessel Wall on the
Velocity of the Molecules .................................................................................................... 15
2.1.4 Dependence of the Number of Impacts with the Vessel Wall on the Volume...................... 15
2.1.5 Mean Velocity of the Molecules – Temperature of a Gas .................................................... 16
2 1.6 Mean Velocity of the Molecules – Influence on Foreign Molecules ................................... 17
2.1.7 Velocity of Molecules in a Gas Compound ......................................................................... 17
2.1.8 Mixing Temperature of Gases .............................................................................................. 18
2.1.9 Increase of Temperature in Gases when Supplying Energy ................................................. 19
2.1.10 Form and Volume Properties of Gases ................................................................................. 20
2.1.11 Adiabatic Compression and Expansion of Gases ................................................................ 21
2.1.12 Dependence of the Pressure on the Temperature ................................................................. 22
2.1.13 Dependence of the Pressure on the Number of Molecules .................................................. 22
2.1.14 Diffusion of Gases................................................................................................................ 23
2.1.15 Diffusion of a Gas through a Porous Partition ..................................................................... 24
2.1.16 Brownian Motion in a Gas ................................................................................................... 25
2.1.17 Density Distribution in a Gas in the Gravitational Field ..................................................... 26
2.1.18 Local Distribution of the Molecules in a Gas ...................................................................... 27
2.2 Structure and Properties of the Liquids ............................................................................. 29
2.2.1 Configuration and Motion of Molecules in a Liquid ........................................................... 29
2.2.2 Increase of Temperature in Liquids when Supplying Energy .............................................. 29
2.2.3 Diffusion of Liquids ............................................................................................................. 30
2.2.4 Brownian Motion in a Liquid............................................................................................... 31
2.2.5 Evaporation of a Liquid ....................................................................................................... 31
2.2.6 Liquefaction of a Gas through Pressure ............................................................................... 32
2.2.7 Solidification of a Liquid ..................................................................................................... 32
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Physical Experiments on the Air-Cushion Table
2.3 Structure and Properties of Solids ...................................................................................... 34
2.3.1 Configuration and Motions of the Lattice Elements in a Solid ............................................. 34
2.3.2 Melting a Solid ....................................................................................................................... 34
2.3.3 Change of the Aggregation State of a Gas through Compression and Cooling ..................... 35
2.3.4 Heat Conduction in Solids ..................................................................................................... 36
2.4 Processes of Electric Conduction ....................................................................................... 37
2.4.1 Motion of an Electron in a Vacuum Under the Influence of an Electric Field
(Demonstrated By Means of Mechanical Forces)................................................................ 37
2.4.2 Deflection of an Electron Radiation in the Electric Field .................................................... 37
2.4.3 Motion of Electrons in a Vacuum Under the Influence of an Electric Field........................ 38
2.4.4 Principle of Electric Conduction .......................................................................................... 39
2.4.5 Influence of Lattice Elements on the Motions of Electrons in an Electric Field ................. 39
2.4.6 Motion of an Electron in a Metal Lattice Under the Influence of the Electric Field
– Ohmic Resistance (Demonstrated By Means of Mechanical Forces)............................... 40
2.4.7 Motion of the Free Electrons in a Metal .............................................................................. 41
2.4.8 Thermal Emission ................................................................................................................ 41
2.4.9 Bound Charge Carriers in an Insulator................................................................................. 42
2.4.10 Behavior of a Free Charge Carrier in an Insulator ............................................................... 43
2.4.11 Electric Conduction in a Semiconductor – Intrinsic Conduction
(Demonstrated By Means of Mechanical Forces)................................................................ 43
2.4.12 Electric Conduction in a Semiconductor – N-Type Conduction
(Demonstrated By Means of Mechanical Forces)................................................................ 44
2.4.13 Electric Conduction in a Semiconductor – P-Type Conduction
(Demonstrated By Means of Mechanical Forces)................................................................ 45
2.5 Nuclear Physics ................................................................................................................... 47
2.5.1 Scattering of Positively Charged Particles Near an Atomic Nucleus .................................... 47
2.5.2 Scattering of Alpha Particles When Passing Through a Metal Foil ...................................... 47
2.5.3 The Rutherford Atomic Model .............................................................................................. 48
2.6 Mechanical Motions............................................................................................................ 49
2.6.1 Vertical, Horizontal and Diagonal Projection ...................................................................... 49
2.6.2 Elastic Collision ................................................................................................................... 49
2.6.3 Change in the Direction of Motion of an Object with a Force ............................................ 50
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Introduction
Physical Experiments on the Air-Cushion Table
Air cushions are produced and sustained by means of air continuously emitted from jets in one of the objects as they move against one an­other. This prevents any contact between the two objects. As a “lubricant”, there is a thin gas cush­ion between them, similar to the oil film frequent­ly used. Due to the much lower viscosity of the air, friction is reduced to negligible levels.
Using the air cushion makes it possible to con­duct many experiments in a much better quality. A large number of experiments, however, are only possible by making use of the air cushion.
A disadvantage of the common two-dimensional air-cushion arrangement is limited visibility. To observe the motions in two dimensions, it is nec­essary to step up closely to the setup. Such sys­tems are furthermore very difficult to handle be­cause of complicated stabilization and adjustment procedures. The use of projection offers new opportunities. It allows both an expedient reduc­tion in the size of all parts of the experiment set­up and a considerable improvement in visibility.
Finally, mechanical collisions proved to be too inefficient. Since in this case only part of the en­ergy is transmitted, it would have been neces­sary to take additional measures to compensate for the loss of kinetic energy. Making use of the forces between ceramic magnets allows the pro­duction of virtually fully elastic collisions. The fact that an immediate contact between the col­liding partners does not occur is no disadvantage in most cases. This method is highly suited for model demonstrations, e.g. of the force relations on a microphysical level.
The gas cushion principle, use of projection and use of magnetic forces make the air-cushion ta­ble a high-quality teaching aid, characterized by simple operation, high reliability, universal us­age and excellent methodological qualities. Some of the experiments basically cannot be carried out better with other currently known methods.
The air-cushion table is used mainly in model demonstrations of microphysical procedures. The characteristic vividness of models and the excel-
lent visibility make this demonstration a kind of “window into the microcosm”. However, it is nec­essary to mind the shortcomings and limits of modeling. Not only are the procedures highly sim­plified and represented in a purely mechanical way, also the motions of the real objects are in many cases determined by other forces. Further­more, all procedures occur on one level. Finally, models contain additional misrepresentations, which become visible e.g. in the shape and color of the hover discs.
Due to the relatively high throughput of air and the small size of the hover discs additional driv­ing mechanisms occur. The effect of these is that the motion of the small, hover discs will not stop as long as the airflow continues. This has the great didactic benefit that many processes can be ob­served for any required duration, without any need of intervention.
On the other hand, the limited force effect be­tween the hover discs and between them and the magnetic barriers determines a specific maximum speed, which, in the case of very quick hover discs, has practically been reached already after one collision.
With the help of these mechanisms, optimal, well­visible motions usually begin by themselves. The driving mechanism increases the velocity; the not fully elastic collisions limit it.
However, both mechanisms can also have an ad­verse effect by misrepresenting the motions of interest. Only the knowledge of these processes and their well directed usage or inclusion by the experimenter allow full utilization of the great potential of this valuable teaching aid.
On the following pages you will find a descrip­tion of the setup and possible uses of the air-cush­ion table. Then you will find instructions for con­ducting important experiments.
The illustrations are meant to assist you in your work. They are taken from the perspective from which the teacher views the experiment setup on the air-cushion table.
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Physical Experiments on the Air-Cushion Table
1. Setup and Possible Uses of the Air-Cushion Table
1.1 Components of the experimenting apparatus
Item Quantity Drawing
Air-cushion table 1
Air source 1
Tube 1
Holding device 1
Lattice model 1
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Physical Experiments on the Air-Cushion Table
Item Quantity Drawing
Plexiglas plate 1
Magnetic barrier 2 253 mm (no. 3 and no. 4)
Magnetic barrier 1 233 mm (no. 2)
Magnetic barriere 1 233 mm with slit for airflow from the side (no. 1)
Magnetic barrier 1 233 mm with opening
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Item Quantity Drawing
Flat magnetic barrier 1
Magnetic barrier made 1 of 4 magnets
Electrodes 2
Manipulating rod 1
Magnetic hover disc 30 Ø 16 mm, red
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Physical Experiments on the Air-Cushion Table
Item Quantity Drawing
Magnetic hover disc 25 Ø 16 mm, green
Magnetic aluminum 5 hover disc, Ø 21 mm
Magnetic hover disc 25 Ø 28 mm, orange
Magnetic hover disc 2 Ø 48 mm, blue
Magnetic piston 1
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Physical Experiments on the Air-Cushion Table
Item Quantity Drawing
Guide piece for the 1 magnetic piston
Fastening screws for 2 the holding device
Plastic tweezers 1
Aufbewahrungskasten 1
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1.2. Principle Uses of the Air-Cushion Table
The system kit allows for
- nearly frictionless movement of the hover discs
- through the air cushion
- modeling the interactions between the mi­croobjects and the field
- through magnetic forces
- through electrical forces
- by tilting the experiment surface
- excellent visibility of all experiments
- due to projection with the overhead projec­tor
- little preparation work
- due to clear and simple system setup
- since only few adjustments required
The experimenter can continually adjust the in­fluence factors and directly intervene in the ex­perimental procedure. All of this ensures a large variety of uses, prefer­ably to demonstrate the behavior of individual microobjects or microobject systems. Therefore it becomes possible to create moving, vivid and highly simplified models of complicated physi­cal objects and phenomena, which one cannot ob­serve directly. Some of the forces taking effect in model exper­iments vary considerably from those occurring between the real objects. In many cases, howev­er, the force-distance relations are very similar, so that special attention only needs to be paid to them in quantitative experiments. Despite this limitation, the air-cushion table is a versatile, effective and appealing teaching aid when handled by a qualified and methodologi­cally skilled experimenter. When teachers have fully understood the operation of the system and follow the operating instructions for the system described below, they can demonstrate experi­ments with physically convincing and effective results.
1.3. Setup of the Air-Cushion Table
air-cushion table is made up of a frame and
The a pressure chamber. The cover plate of the pres-
sure chamber has 1089 holes (ø 0.8 mm). This is the experiment surface. The side of the pressure
Physical Experiments on the Air-Cushion Table
chamber where the impulse valve is located is connected to the fan using the tube. The experi­ment surface can be set to the horizontal or in­clined position by means of two adjusting screws.
.
. Five different types of with the air-cushion table. They are made of col­ored, transparent plastic or aluminum discs, onto which cylindrical, ceramic magnets are attached. Carried by the air cushion, these hover discs sim­ulate the moving objects. The experiment surface is delimited by a flat plas­tic frame. It is also possible to attach magnetic barriers allowing for almost fully elastic colli­sions of the hover discs. Therefore it becomes possible to demonstrate interactions with the ves­sel walls. To create an electric field, two rod-type electrodes can be placed on the experiment surface. A mod­el effect of an electric field can also be attained by inclining the air-cushion table to the desired degree. The impulse valve can be used to create an air­flow parallel to the experiment surface influenc­ing the motion of the hover discs. This can be used to increase the speed of the hover discs. The fan ensures a sufficient air cushion over the experiment surface. Its performance is continu­ously adjustable and can be adapted to the condi­tions of the experiment. The fan is equipped with a delivery connection and a suction connection. While experimenting with the air-cushion table, the delivery connection is used, the suction con­nection can be used for other physical experi­ments (e.g. with the transparency panel appara­tus). The lattice model is made up of 25 ceramic mag­nets, which are suspended by thin steel wires. This system oscillates with little absorption. It is used to demonstrate e.g. the interaction of a metal lat­tice with the moving charge carriers as a model. It is inserted into the holding device in the same way as the Plexiglas plate. The height in which these components are located above the experi­ment surface can be adjusted as individually suit­ed for each experiment by means of the setscrew. The settings can be easily reproduced using the scale marks.
hover discs are supplied
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1.4. Instructions for Usage
The air-cushion table is placed onto the overhead projector so that the arrow on the pressure cham­ber points to the projection screen. The magnetic barriers (fig. 1) are placed onto the air-cushion table so that their numbers (no. 1 to no. 4) match the markings at the edges of the experiment sur­face. The magnetic barrier with the slit at the bottom is arranged at the side of the table where the tube of the fan connects. The air flows through the slit and over the experiment surface when activating the impulse valve. The pressure chamber and the fan are connected by the tube (fig. 2). The tube should run as straight as possible. Only one position is possible when connecting it to each of the devices. This is why both ends of the tube and the connectors of the devices are marked with a line. The tube is con­nected to the device so that both lines meet. Then it is turned slightly to the right or to the left. Next, the experiment surface is aligned horizon­tally by means of the adjusting screws at sides 2 and 4 by means of the spirit levels. When needed, the impulse valve is pressed sev­eral times for approx. 1 second. The fan has to be set to a sufficient performance level, since other­wise the pressure of the air cushion is too low and the hover discs will sink onto the experiment surface. To install the lattice model, the holding device is screwed onto the frame of the air-cushion table. The lattice model is then inserted into the groove of the holding device (fig. 3) The influence of the lattice model on the motion of the hover discs
strongly depends on the height of the lattice over the experiment surface. The holding device, which is marked with a scale (fig. 4) can be infi­nitely adjusted to the appropriate height using a setscrew. This allows for demonstrations of the behavior of conductors, semi-conductors and insulators. The electrodes are used to create an electric field. They can be applied in two positions. Placing them onto their base will create a gap between the experiment surface and the electrodes. This gap is large enough for the aluminum hover discs to fit through. These are then charged in accor­dance with the polarity of the respective electrode. The electrodes can also be turned around so that their bases point upwards. Then the aluminum parts touch the experiment surface and the hover discs contact the electrodes. The voltage applied should be over 20 000 V. When the voltage is lower, the electrodes have to be arranged closer to each other. An especially well-suited voltage source is the electrostatic generator. The influence of the electric field on the motion of the hover discs can also be demonstrated by slightly tilting the experiment surface. The de­gree of inclination then corresponds to the strength of the electric field. The strength of the fan is adjusted until the hover discs just begin to move freely. This ensures a relatively low level of noise. When the airflow is stronger, disturbance caused by the noise of the fan cannot be avoided. For this reason, it should
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Physical Experiments on the Air-Cushion Table
be positioned behind the experimenting table or inside it. This will reduce the noise level reach­ing the classroom. Further be reached by wrapping sponge rubber around the fan or lining it with Piatherm or the like. Spe­cial care should be taken, though, to ensure that the air can enter the suction nozzle unimpeded.
1.5. Maintenance and Care
The air-cushion table is a high-quality appara­tus, which requires special care. Its stability has certain limits because of the consistency of the necessarily transparent material.
noise reduction can
- Avoid damage caused by dropping, hitting, bumping, dragging or sliding.
- Keep all parts clean and free from dust.
- Remove dust with an anti-static cloth. Strong rubbing of the table surface causes electro­static charging which may considerably affect the experiments.
- To keep the pressure chamber clean, do not place the airflow generator near dust accumu­lations.
- Keep the bottom sides of the hover discs clean at all times. They can be easily cleaned using ethyl alcohol.
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Physical Experiments on the Air-Cushion Table
2 Description of the Experiments
2.1 Structure and Properties of Gases
2.1.1 Motion of a Molecule in High Vacuum
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Hover discs l Piece
Model simulation
Real Object Model
Vessel containing Experiment surface of the gas the air-cushion table Walls of the vessel Magnetic barriers Gas melecules Hover discs
How to proceed:
Align the air-cushion table horizontally and attach the magnetic barriers. Turn the fan to a medium setting. Place the hover disc onto the experiment surface and give it an impact so that it hits a magnetic barrier in the middle at an angle of 45°.
Result:
The motion of the hover disc is straight and uni­form. When it hits a barrier, the direction of its motion changes. The speed is unchanged. The hover disc rebounds at the same angle at which it hits the barrier. The law of reflection applies.
2.1.2 Motion of the Molecules in a Gas
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Hover disc, red 16 Pieces
Model simulation
Real Object Model Vessel containing Experiment surface of the gas the air-cushion table Walls of the vessel Magnetic barriers Gas molecules Hover discs
How to proceed:
Align the air-cushion table horizontally and attach the magnetic barriers. Place the 16 red hover discs anywhere on the experiment surface so that the spaces between them are approximately 1 cm. Then turn the fan to a setting in which all hover discs are sure to lift off.
Result:
Each hover disc moves in a straight and uniform way as long as it does not hit any other hover disc or a magnetic barrier. When two hover discs collide, their speed and direction of velocity usually changes. These collisions cause a transmission of kinetic energy. When hitting the magnetic barrier, only the direction of velocity changes.
Interpretation:
The gas molecule moves in accordance with the laws of classical mechanics.
Interpretation:
Elastic collisions occur between the molecules of a gas and when molecules hit the vessel wall. Along the distance covered between two colli­sions, the “free length of path”, the motion of the molecules is straight and uniform.
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Note:
This experiment can be developed from the one described above in 2.1.1. by placing three additional orange hover discs onto the experiment surface one after the other while keeping the fan turned on. The collisions between the discs and the transfer of kinetic energy caused by them can be especially well observed when using a low number of discs.
2.1.3 Dependence of the Number of Impacts with the Vessel Wall on the Velocity of the Molecules
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Hover discs 2 Pieces Stop watch or master clock l Piece
Physical Experiments on the Air-Cushion Table
Note:
The hover disc can also be set into motion so that it hits the barriers at a perpendicular angle.
Model simulation
Real Object Model
Vessel containing Experiment surface of the gas the air-cushion table Walls of the vessel Magnetic barriers Gas molecules Hover discs
How to proceed:
After aligning the air-cushion table horizontally, attach the magnetic barriers. Turn the fan to a setting in which two hover discs placed above each other are sure to lift off. Give this doubled hover disc an impact so that it hits one of the barriers in the middle at an angle of 45°. Count the impacts with the wall occurring within a given period of time (10 seconds). Then repeat the experiment with only one of the hover discs at a higher velocity.
Result:
The higher the velocity of the hover disc is, the more often it will hit the magnetic barrier within a specific period of time.
Interpretation:
The higher the velocity of the molecules is, the more impacts of the gas molecules will occur with the vessel wall. Since these impacts cause the pressure, higher molecule velocities cause high­er pressure.
2.1.4 Dependence of the Number of Impacts with the Vessel Wall on the Volume
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Hover disc, red l Piece Hover disc, grün l Piece Stop watch or master clock
Model simulation
Real Object Model
Vessel containing Experiment surface of the gas the air-cushion table
surrounded by magnetic
barriers Walls of the vessel Magnetic barriers Gas molecules Hover discs
How to proceed:
Align the air-cushion table horizontally and attach the magnetic barriers. Turn the fan to a setting in which the hover discs are sure to lift off. Then place both hover discs into one corner of the experiment surface, first holding them with two fingers and then quickly releasing them. Count the number of impacts one of the discs performs with the vessel walls within a specific period of time (5 seconds).
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Then reduce the area available for the hover discs to half its size. To do this, lift up magnetic barrier no. 2 and reattach it so that it separates the experiment surface into two halves, with its ends snapping into the recesses provided in barriers no. 3 and no. 4. Now set both hover discs into motion in the same way. Count the number of impacts one of the hover discs performs with the magnetic barriers within the same period of time as in the previous experiment.
Result:
In the first experiment, the number of impacts with the barriers is lower than in the second. By reducing the area to half its size, the number of impacts increases to approximately the double amount.
Interpretation:
Reducing the volume of a vessel containing a gas causes an increase in the number of impacts of the gas molecules with the vessel walls within a specific period of time. Since the number of im­pacts occurring in a specific period of time with a specific wall is an indicator of pressure, the conclusion is that reducing the volume increases the pressure.
Note:
Evaluation is easier when counting only the impacts with magnetic barrier no. 2 in each of the experiments. This, however, requires longer times of measurement. It is also possible to ascertain the total amount of impacts of both discs. In this case it is recom­mended that one student counts the impacts of the red disc while another student counts those
of the green. The results are then added up.
2.1.5 Mean Velocity of the Molecules – Temperature of a Gas
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Hover discs, red 16 Pieces
Model simulation
Real Object Model
Vessel containing Experiment surface of the gas the air-cushion table Walls of the vessel Magnetic barriers Gas molecules Hover discs
How to proceed:
Align the air-cushion table horizontally and attach the magnetic barriers. Position all hover discs in one corner of the experiment surface so that the spaces between them are approximately 1 cm. The fan is turned to a medium setting. Sequentially observe the motions of each of the hover discs. Draw attention to the velocity of each disc in relation to the velocity of all other discs. Gradually turn down the fan so that all hover discs come to a stop and then turn it up again so that they are sure to lift off. The same observations are repeated at a lower velocity.
Result:
The velocity of each hover disc changes with each impact. While an impact with the vessel wall
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causes only a change in direction, a collision of two hover discs usually causes a change in speed as well. At any given point in time, the majority of the hover discs move at a mean velocity. Only few hover discs have a high and few a very low velocity.
Interpretation:
The molecules in a gas have different velocities. The velocity of each gas molecule changes with each impact. Many molecules move at a velocity that is close to the mean velocity. Only few mole­cules have a very low or high velocity. The distri­bution of velocity is constant over time in a large number of molecules. The mean kinetic energy of the molecules characterizes the temperature of the gas. A low mean kinetic energy corresponds to a low temperature, a large mean kinetic energy to a high temperature. In each case there are mole­cules whose velocity is very low and others which are especially fast.
Note:
To ensure better visibility of the motions of a specific hover disc, use 15 red hover discs and 1 green one rather than 16 red ones.
Model simulation
Real Object Model
Vessel containing Experiment surface of the gas the air-cushion table Walls of the vessel Magnetic barriers Gas molecules Green hover disc Foreign gas Red hover disc molecule
How to proceed:
Align the air-cushion table horizontally and attach the magnetic barriers. Closely arrange the green hover discs in one corner of the experiment surface so that the spaces between them are approximately 1 cm. Turn up the fan so that all hover discs are sure to lift off. Place the red hover disc in the middle of the experiment surface, holding it with the finger and then releasing it so that it is not in motion at first. Observe the motion it subsequently performs. Then place the red hover disc directly into one corner of the experiment surface, holding it with the pointer and then quickly releasing it so that it moves in the direction of the center at high velocity.
Result:
In the first experiment, the red hover disc repeatedly receives impacts from the green discs. Its motion then no longer differs from that of the others. In the second experiment, the velocity of the red hover disc is reduced by collisions with the green ones, so that its motion then also corresponds to theirs.
Interpretation:
If a foreign gas molecule penetrates into a gas it cannot continue in its state of motion. The inter­action with the other gas molecules adapts its motion to theirs after a short time.
2 1.6 Mean Velocity of the Molecules
– Influence on Foreign Molecules
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Hover disc, green 12 Pieces Hover disc, red l Piece
2.1.7 Velocity of Molecules in a Gas Compound
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Hover disc, red 12 Pieces Hover disc, orange 2 Pieces
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Model simulation
Real Object Model
Vessel containing Experiment surface of the gas the air-cushion table Walls of the vessel Magnetic barriers Gas molecules Red hover disc with small mass Gas molecules Orange Hover discs with large mass
How to proceed:
Align the air-cushion table horizontally and attach the magnetic barriers. Place the hover discs anywhere onto the experiment surface, so that the spaces between them are not much more than 1 cm. Turn the fan up to a setting at which all hover discs are sure to lift off. Observe the motions of both types of hover discs with regard to their velocity.
Result:
The mean velocity of the orange hover disc is much lower than the mean velocity of the red ones.
Interpretation:
In a compound of two gases whose molecules have different masses, the molecules have differ­ent mean velocities. The molecules with the less­er mass move much faster than those with the greater mass. Since the temperature of the gas compound cor­responds to the mean kinetic energy of
all mole-
cules, the mean kinetic energy of the molecules
2
1
Emv
with the lesser mass
=
has to be equal to
k
kk
2
the mean kinetic energy of the molecules with the
2
1
Emv
greater mass
=
This leads to the conclu-
g
gg
2
sion that in a gas compound of a given tempera­ture the molecules of different masses have dif­ferent mean velocities.
2.1.8 Mixing Temperature of Gases
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Magnetic piston l Piece Guide piece for the l Piece magnetic piston Hover disc, orange 4 Pieces
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Physical Experiments on the Air-Cushion Table
Model simulation
Real Object Model
Vessel containing Experiment surface the gas of the air-cushion Walls of the vessel Magnetic barriers Partition Magnetic piston Gas molecules Hover discs
How to proceed:
Align the air-cushion table horizontally and attach the magnetic barriers. Divide the experiment surface in half using the magnetic piston, paral­lel to the barriers nos. 1 and 2. For guidance of the piston rod, place the guide piece for the magnetic piston onto barrier no. 2. Place two hover discs into each half. Increase the fan setting so that both hover discs are sure to float even when the impulse valve is opened. Open the impulse valve repeatedly in order to set the hover discs in the adjacent half of the experiment surface into strong motion, while ensuring lesser motion of the other two discs, if necessary by slowing them down manually. Now quickly remove the magnetic piston from the experiment surface and observe the motion of all hover discs.
the resulting temperature is between the two ini­tial temperatures. The reason for this is that the molecules of the gas with the higher temperature transfer part of their kinetic energy to the mole­cules of the gas with the lower temperature.
Note:
The experiment can also be carried out with 8 green and 8 red hover discs. This is a better dem­onstration of the conditions in a gas due to the larger number of hover discs. However, it is more difficult to maintain the difference in velocity. For this reason, it is necessary to (manually) accelerate the hover discs in one half and to slow them down in the other.
2.1.9 Increase of Temperature in Gases when Supplying Energy
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Hover disc, red 12 Pieces Hover disc, green 4 Pieces
Result:
The fast discs partially transfer their energy onto the slow ones. The mean velocity of all four hover discs is lower after the removal of the piston than the velocity of the two fast discs in the one half and higher than that of the two slow ones in the other half.
Interpretation:
When mixing two gases of different temperatures,
Model simulation
Real Object Model
Vessel containing Experiment surface the gas of the air-cushion Walls of the vessel Magnetic barriers Gas molecules Red hover disc Molecules with Green hover disc higher energy
How to proceed:
After aligning the air-cushion table horizontally,
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attach the magnetic barriers and spread the red hover discs evenly on the experiment surface. Provide an airflow just ensuring that all hover discs lift off. This keeps the mean velocity of the red discs low. Shortly afterwards, make the 4 green hover discs shoot between the red ones at the highest possible speed. This can be done in quick succession from one corner, using the pointer to hold each hover disc directly in the corner and then quickly releasing it. It is also possible to press all 4 hover discs against a barrier at the same time, holding them with the fingers and then releasing them so that they hit the red hover discs at high speed.
Result:
The green hover discs shooting in at high speed cause a noticeable increase of the mean velocity of the red hover discs.
2.1.10 Form and Volume Properties of Gases
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Magnetic piston l Piece Hover disc, green 12 Pieces
Model simulation
Real Object Model
Vessel containing Experiment surface of the gas the air-cushion table
surrounded by the magnetic barriers and
the magnetic piston Walls of the vessel Magnetic barriers Piston to change the Magnetic piston form and volume of the area available for the gas Gas molecules Hover disc
Interpretation:
When supplying energy to a gas, its temperature will rise. The energy supply can be interpreted as shooting in of particles with high velocity, mixing with a gas of higher temperature or heating.
Note:
Energy can also be supplied by repeatedly opening the impulse valve for a short time. To ensure that the hover discs will float safely even when the valve is opened, a stronger airflow will be necessary. To repeat the experiment, slowly reduce the airflow until the motions stop and then return to the original setting.
How to proceed:
Align the air-cushion table horizontally and attach the magnetic barriers. Attach the magnetic piston to divide the experiment surface in two halves. Closely arrange the hover discs in one half so that the spaces between them are not much more than 1 cm. The fan is turned up to a setting in which all hover discs are sure to lift off. The area available for the hover discs is increased by quickly removing the piston. The piston is placed back onto the experiment surface near a barrier and its rod is moved back and forth to the right and left so that the shape of the experiment surface available for the hover discs changes. Observe the reaction of the hover discs to the change in area in both cases.
Result:
In both experiments, the hover discs completely fill out the available area. They are quickly dis­persed across the entire area.
Interpretation:
In beiden Experimenten füllen die Hover disc die zur Verfügung stehende Fläche voll aus. Sie verteilen sich dabei schnell auf die ganze Fläche.
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Note:
The experiments can be repeated using different initial positions of the piston and different mean velocities of the hover discs. The more closely the discs are arranged at the beginning and the higher their mean velocity is, the quicker they will fill out the entire area.
2.1.11 Adiabatic Compression and Expansion of Gases
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Magnetic piston 1 Pieces Guide piece for magnetic piston l Piece Hover disc, red 10 Pieces
Model simulation
Real Object Model
Vessel containing Experiment surface of the gas the air-cushion table
surrounded by the magnetic barriers and
the magnetic piston Walls of the vessel Magnetic barriers Piston to change the Magnetic piston volume of the gas Gas molecules Hover disc
between them are approximately 2.5 cm. Then increase the fan setting so that all hover discs are floating properly. Rapidly move the piston to the opposite side so that the area available for the hover discs is reduced to approximately one fifth. Observe the motion of the hover discs with regard to velocity and impacts. Then increase the area in the same way by moving the piston back. Observe the motion of the hover discs again.
Result:
When reducing the size of the area both the mean velocity of the hover discs and the number of impacts among each other and with the barriers increase. When increasing the area, their mean velocity decreases and the number of impacts is reduced.
How to proceed:
Align the air-cushion table horizontally and attach the magnetic barriers. Place the piston at the edge of the experiment surface. To guide the piston rod, place the guide piece for the magnetic piston onto barrier no. 2. Spread the 10 hover discs across the experiment surface so that the spaces
Interpretation:
Quick compression of a gas increases the mean
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velocity of the molecules and the number of im­pacts. The temperature and pressure of the gas increase. When expanding a gas adiabatically, the mean velocity of the molecules decreases and there is a drop in pressure and temperature.
2.1.12 Dependence of the Pressure on the Temperature
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Magnetic piston l Piece Guide piece for magnetic piston l Piece Hover discs 8 Pieces
Model simulation
Real Object Model
Vessel containing Experiment surface of the gas the air-cushion table
surrounded by the magnetic barriers and
the magnetic piston Walls of the vessel Magnetic barriers Piston limiting the Magnetic piston volume of the gas Gas molecules Hover disc
How to proceed:
Align the air-cushion table horizontally and attach the magnetic barriers. Place the piston on the experiment surface parallel to magnetic barrier no. 2. To provide a lateral boundary for the piston rod and to ensure its successful guidance, place the guide piece for the magnetic piston onto barrier no. 2. Place the hover discs onto the experiment surface near barrier no. 1 with the slit for the airflow entering the experiment surface from the side. Move the piston towards this barrier as far as possible. Turn the fan to a setting that provides a strong airflow. Increase the mean velocity of the hover discs by repeatedly opening the impulse valve for a short period. Observe the motions of the hover discs and the piston.
Result:
The piston shifts through the impacts of the hover discs at the rate at which the mean velocity of the hover discs rises. This causes an enlargement of the area available to the hover discs.
Interpretation:
Increasing the temperature of a gas causes a rise in pressure when the volume is constant. If the vessel containing the gas is equipped with a mov­ing piston, a rise in temperature will increase the volume of the gas.
Note:
The force acting on the piston from the outside due to air pressure can also be demonstrated in this experiment by slightly tilting the experiment surface so that the hover discs have to push the piston up a slope.
2.1.13 Dependence of the Pressure on the Number of Molecules
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Magnetic piston l Piece Guide piece for the magnetic piston l Piece Hover discs 8 Pieces
Model simulation
Real Object Model
Vessel containing Experiment surface of the gas the air-cushion table
surrounded by the magnetic barriers and
the magnetic piston Walls of the vessel Magnetic barriers Piston limiting the Magnetic piston volume of the gas Gas molecules Hover disc
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How to proceed:
Align the air-cushion table horizontally and attach the magnetic barriers around the experiment surface. Arrange the piston parallel to magnetic barrier no. 2. The piston rod rests on the guide piece for the magnetic piston, which has been attached onto magnetic barrier no. 2 and ensures its guidance. Arrange three of the hover discs near barrier no. 1, the barrier with the slit for air ente­ring from the impulse valve. Move the piston as far as possible towards this barrier. Turn the fan to a setting providing a strong airflow. Now bring one of the remaining discs after the other onto the experiment surface, making each shoot in at the highest possible speed starting from barrier no. 1. Observe the motions of the hover discs and the piston.
Result:
The piston shifts through the impacts of the hover discs at the rate at which the number of discs increases. This causes an enlargement of the area available to the hover discs.
Interpretation:
Increasing the number of molecules in a specific gas volume causes a rise in pressure. If the ves­sel containing the gas is equipped with a moving piston, the volume of the gas will increase when the number of molecules rises.
Note:
It is also possible to demonstrate the force acting on the piston from the outside due to air pressure. This is done by slightly tilting the experiment surface so that the hover discs have to push the piston up a slope to increase the area in size.
2.1.14 Diffusion of Gases
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Magnetic piston l Piece Hover disc, red 6 Pieces Hover disc, green 6 Pieces
Model simulation
Real Object Model
Vessel containing Experiment surface the gas of the air-cushion table Walls of the vessel Magnetic barriers Partition Magnetic piston Molecules of Green hover disc one gas Molecules of the Red hover disc other gas
How to proceed:
Align the air-cushion table horizontally and insert the magnetic barriers. Place the red discs in one half of the experiment surface, near magnetic barrier no. 1, and the green discs in the other half, near barrier no. 2. Place the magnetic piston in the center as a partition running parallel to barriers no. 1 and 2. Turn the fan to a low setting so that the hover discs just lift off. Then quickly remove the piston and observe the motions of the red and green discs. Repeat the experiment using a stronger airflow after placing the red discs close to barrier no. 1 and the green ones close to barrier no. 2.
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Result:
After removing the partition, the hover discs mix evenly as a result of their own motions. This will occur more rapidly the higher the mean velocity is.
Interpretation:
When removing the partition separating two gas­es contained in a vessel, these gases will mix by themselves (diffusion). This process is caused by the thermal motion of the molecules. The higher the temperature, the higher the diffusion speed. The reason for this is the higher velocity of the molecules at higher temperatures. As a result of diffusion, the system changes from a state of a higher order to that of a lower order. The entropy increases.
2.1.15 Diffusion of a Gas through a Porous Partition
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Magnetic barrier with opening l Piece Hover disc, green 4 Pieces Hover disc, red 6 Pieces
Model simulation
Real Object Model
Vessel containing Experiment surface die Gase befinden of the air-cushion table Walls of the vessel Magnetic barriers Porous partition Magnetic barrier with
opening Molecules of one gas Red hover disc Molecules of the Green hover disc other gas
How to proceed:
Align the air-cushion table horizontally and attach the magnetic barriers. The magnetic barrier with the opening divides the experiment surface in two halves with its ends latching into the recesses pro­vided in barriers nos. 3 and 4. The red discs are placed in the half that is delimited by magnetic barrier no. 1 with the slit for the airflow entering from the side. Select the lowest possible airflow at which the discs are sure to float and observe their movement through the opening of the middle barrier. Repeat the experiment using a stronger airflow, increasing the mean velocity of the hover discs by repeatedly opening the impulse valve for a short time, as opposed to the first experiment. For the next experiment, place 4 green discs in one half of the experiment surface and 4 red ones
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in the other. After turning the fan on, observe the movement of the hover discs through the opening. Increase the mean velocity of the hover discs by repeatedly opening the impulse valve for a short time.
Result:
In all experiments hover discs move through the opening at irregular intervals. As a result in the first two experiments, each half contains approximately the same amount of discs after some time. In the last experiment the hover discs penetrate the opening in both directions, so that both types of discs mix. These procedures will occur more rapidly the higher the mean velocity of the hover discs is.
Interpretation:
The molecules of a gas can penetrate a porous partition. If the gas is initially contained in one chamber of a vessel with a porous partition, the diffusion through the partition causes an equal­ization of pressure so that eventually both cham­bers contain the same amount of molecules. If the two chambers of a vessel divided by a porous par­tition contain different gases, these gases will mix through the partition. Diffusion will occur more rapidly the higher the temperature of the gases is.
2.1.16 Brownian Motion in a Gas
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Hover disc, red 16 Pieces Hover disc, blue l Piece
Model simulation
Real Object Model
Vessel containing Experiment surface the gas of the air-cushion Walls of the vessel Magnetic barriers Gas molecules Red hover discs Particle showing the Blue hover disc Brownian motion
How to proceed:
Align the air-cushion table horizontally and attach the magnetic barriers around the experiment surface. Arrange the red discs near the magnetic barriers of the air-cushion table. Place the blue disc at the center of the experiment surface. Set the fan to a medium setting. Observe the motions of the blue disc.
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Result:
The red discs hit the blue one at irregular intervals, setting it into motion. Its speed and direction of velocity change permanently, resulting in a zigzag path. Its average speed over time is much lower than that of the red discs.
barriers. Turn the fan to a medium setting. Use the adjusting screw on barrier no. 4 to tilt the experiment surface of the apparatus more and more towards the projecting wall. Observe the changing distribution of the hover discs on the experiment surface.
Result: At first, the hover discs are evenly distributed across the entire experiment surface. As the in­clination increases, the density of the hover discs decreases from the bottom to the top.
Interpretation:
Small particles (dust, smoke particles, water droplets), which are visible under the microscope, perform a Brownian motion in gases. It is caused by the disordered motion of the gas molecules.
2.1.17 Density Distribution in a Gas in the Gravitational Field
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Hover disc, red 20 Pieces
Model simulation
Real Object Model
Part of the earth’s Experiment surface atmosphere of the air-cushion table Gas molecules in the Hover discs earth’s atmosphere
Gravitational field Inclination of the
experiment surface
How to proceed: Align the air-cushion table horizontally and attach the magnetic barriers on the experiment surface. Arrange the hover discs near the magnetic
Interpretation:
Where gases are contained in the gravitational field of the earth, the density of the gas decreas­es with increasing distance to the earth’s surface.
Note:
The experiment can also be evaluated quantitatively. Divide the experiment surface e.g. in 5 parallel horizontal strips of equal width. This can be done by drawing lines on a transparency inserted under the air-cushion table. Turn off the fan and count the number of discs contained in each strip. When the average numbers of discs contained in each strip calculated in several measurements are depicted graphically as a function of height, the slope of the graph will be nearly exponential. The deviations occur because each hover disc takes up a relatively large area and the repulsive forces have a noticeable influence on the motion even from a distance of several centimeters.
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2.1.18 Local Distribution of the Molecules in a Gas
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Manipulating rod 1 Piece Hover disc, red 4 Pieces Stop watch or master clock
Model simulation
Real Object Model
Vessel containing Experiment surface the gas of the air-cushion Walls of the vessel Magnetic barriers Halves of the vessel Halves of the
experiment surface
Gas molecules Hover discs
Physical Experiments on the Air-Cushion Table
and finally, considerably less often, the 4:0 and 0:4 distributions. The frequencies of the 3:1 and 1:3 distributions are approximately equal, as are the 4:0 and 0:4 distributions.
How to proceed:
After aligning the air-cushion table horizontally, attach the magnetic barriers at the edges of the experiment surface. The experiment surface is divided in half by placing the manipulating rod onto the middle of barriers nos. 3 and 4. Spread the discs anywhere across the experiment surface and turn the fan to a medium setting. Increase the motion of the hover discs to a high mean velocity by repeatedly opening the impulse valve for a short time. When a specified period of time has elapsed, examine the distribution of the 4 hover discs in both spaces. This is done by covering the connector opening of the fan with the hand. Record the calculated distribution in table 1. Then release the opening again and open the impulse valve several times. Cover the opening again after the specified period of time, record the distribution, etc. Depict the relative frequency of each possible distribution in a bar chart after 20 experiments, 40 experiments, etc. (Fig. 5)
Result:
Although the hover discs move in a completely disorderly fashion, the result obtained from a large number of experiments is that the distribution across both halves is subject to certain rules. The distribution occurring most frequently is 2:2, followed by the 3:1 and 1:3 distributions
Interpretation:
The distribution of the molecules in a gas is gov­erned by the laws of statistics. In the case of 4 molecules distributed onto 2 half spaces, the 0:4, 1:3, 2:2, 3:1 and 4:0 distributions occur at a ra­tio of 1 : 4 : 6 : 4 : 1. This corresponds to the relative frequencies of 6.25 % : 25 % : 37.5 % : 25% : 6.25%.
Note:
An easier method to determine the individual distributions is to calculate and record the distribution after a specified period of time (e.g. 5 seconds). It is sufficient to observe only one half of the experiment surface and to determine how many hover discs it contains at the specified points in time. The number of hover discs contained in the other half is obtained by deduction from 4.
The ratio of distributions given above is applicable under the assumption that the molecules have a very low volume and that the repulsive forces are effective only in the imme­diate proximity of the molecules. These conditions are not given in the case of the hover discs used for demonstration. This is why the 2:2 distribution is overrepresented in the experiment, while the other distributions occur less often than expected.
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Table 1
Distribution 0 : 4 1 : 3 2 : 2 3 : 1 4 : 0
Relative frequency in % 5 20 49 21 5
Relative frequency in %
40
20
0
:::::4132231400
Distribution
Fig. 5: Relative frequency of the distributions in 100 experiments
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2.2 Structure and Properties of the Liquids
2.2.1 Configuration and Motion of Molecules in a Liquid
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Hover disc, orange 25 Pieces
Model simulation
Real Object Model
Vessel containing Experiment surface of the liquid the air-cushion table Walls of the vessel Magnetic barriers Molecules of the Hover discsHover discs liquid
How to proceed:
Align the air-cushion table horizontally. First place the magnetic barriers on the experiment surface and next the hover discs. Turn the fan to a setting in which the hover discs are sure to float even when the impulse valve is opened. Briefly open the impulse valve several times so that the mean velocity of the discs is as high as possible. Observe the arrangement and motion of the hover discs.
Result:
The hover discs are irregularly arranged at short distances. Each hover disc performs oscillating and circular motions around its location. However, it is not bound to any specific location, rather changing it at irregular intervals or moving
on between the other discs. The kinetic energy differs from disc to disc and changes from time to time in each disc. The hover discs are irregularly arranged at short distances. Each hover disc performs oscillating and circular motions around its location. However, it is not bound to any specific location, rather changing it at irregular intervals or moving on between the other discs. The kinetic energy differs from disc to disc and changes from time to time in each disc.
Interpretation:
The molecules of a liquid are in permanent, irre­gular motion, with prevailing oscillating and cir­cular motions around the respective location. In almost every molecule these motions are tem­porarily superimposed by irregular translatio­nal movements. The kinetic energy of the indivi­dual molecules varies and is constantly changing.
2.2.2 Increase of Temperature in Liquids when Supplying Energy
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Hover disc, orange 25 Pieces
Model simulation
Real Object Model
Vessel containing Experiment surface of the liquid the air-cushion table Walls of the vessel Magnetic barriers Molecules of the Hover discs liquid
How to proceed:
Align the air-cushion table horizontally and attach the magnetic barriers. Place the hover discs on the experiment surface. Turn the fan to setting in which the hover discs are sure to lift off. Initially, the velocity of the hover discs has to be kept low by briefly opening the impulse valve at rather long intervals. Gradually increase the velocity by opening the valve at shorter intervals. Observe the motion of the hover discs.
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Result:
As an increased amount of energy is supplied, the motion of the hover discs becomes stronger. They perform their oscillating motions at higher amplitudes, exchange their locations more frequently and move from one place to another at higher speed.
Interpretation:
When supplying energy to a liquid, the mean ki­netic energy of the molecules increases. The tem­perature rises.
2.2.3 Diffusion von Flüssigkeiten Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Hover disc, red 20 Pieces Hover disc, green 20 Pieces
Model simulation
Real Object Model
Vessel containing Experiment surface of the liquid the air-cushion table Walls of the vessel Magnetic barriers Molecules of Red hover discs one liquid Molecules of the Green hover discs other liquid
How to proceed:
Align the air-cushion table horizontally and place the magnetic barriers on the experiment surface. Spread the hover discs evenly across the entire experiment surface so that all green discs are arranged in one half and all red ones in the other half and the line dividing them runs parallel to barriers nos. 1 and 2. Turn the fan to a setting in which the hover discs are sure to float even when opening the impulse valve. Observe the motions of the hover discs, especially in the area around the borderline.
Result:
The hover discs gradually mix in the area of the borderline as a result of the occasional translational motions. With time, more and more red discs move into the area of the green ones and vice versa. After some time, the discs have mixed completely.
Interpretation:
The disordered motions of the molecules causes the liquids to mix by themselves. Due to the low translation speed the diffusion in liquids occurs much slower than in gases.
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2.2.4 Brownian Motion in a Liquid
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Hover disc, orange 25 Pieces Hover disc, blue l Piece
Model simulation
Real Object Model
Vessel containing Experiment surface of the liquid the air-cushion table Walls of the vessel Magnetic barriers Molecules of Orange hover discs the liquid Particle showing the Blue hover disc Brownian motion
How to proceed:
Align the air-cushion table horizontally and attach the magnetic barriers. Arrange the orange discs near the magnetic barriers of the air-cushion table. Place the blue disc at the center of the experiment surface. While the impulse valve is opened, turn up the fan so that all hover discs lift off. Then briefly open the impulse valve every now and then. Observe the motion of the blue disc interacting with the orange ones.
Result:
Repeated impacts of the orange discs cause a disordered motion of the blue disc. Its mean ve­locity over time is much lower than the mean velocity of the orange discs.
Interpretation:
If a liquid contains microscopically small par­ticles the thermal motion of the invisible mole­cules sets them into an irregular motion which can be observed under the microscope.
2.2.5 Evaporation of a Liquid
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Holding device 1 Piece Plexiglas plate 1 Piece Flat magnetic barrier 1 Piece Hover disc, green 10 Pieces
Model simulation
Real Object Model
Vessel containing Experiment surface of the liquid the air-cushion table Walls of the vessel Magnetic barriers Surface of the liquid Flat magnetic barrier Molecules of Hover discs the liquid
How to proceed:
Align the air-cushion table horizontally and attach the magnetic barriers. Then tilt the experiment surface by screwing in the adjustment screw on barrier no. 4. Arrange the hover discs on the half of the experiment surface adjacent to barrier no.
3. Fasten the holding device to the air-cushion
table and insert the Plexiglas plate. Place the flat magnetic barrier onto the Plexiglas plate so that it runs parallel to the magnetic barriers nos. 3 and 4, below the center. The magnetic strip should face down, with the arrow pointing to the projecting wall. Then set the plate to the lowest position. Turn the fan to a medium setting. Observe the behavior of the hover discs, especially those near the flat magnetic barrier. Then gradually increase the mean velocity of the hover discs by briefly opening the impulse valve several times.
Result:
The slow hover discs cannot exit the lower part of the experiment surface. The faster ones, how­ever, cross this border and reach the upper section of the experiment surface. Here they move in a straight and uniform way until hitting other hover discs or the magnetic barrier. Occasionally, discs will also return to their original space.
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The larger the mean velocity of the hover discs is, the faster individual discs will leave the origi­nal section.
Interpretation:
A liquid contains molecules of different veloci­ties at all times. The fastest among these molecu­les succeed in leaving the liquid. This process of evaporation also occurs beneath the boiling tem­perature of the liquid. Since molecules from the gas atmosphere also return into the liquid, a dy­namic equilibrium state is soon reached. The speed of evaporation increases as the tem­perature rises.
Note:
The inclination of the experiment surface simulates the gravitational field. This makes more particles return from the gas phase into the liquid phase.
2.2.6 Liquefaction of a Gas through Pressure
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Magnetic piston 1 Piece Guide piece for the magnetic piston l Piece Hover disc, red 20 Pieces
Model simulation
Real Object Model
Vessel containing Experiment surface of the liquid the air-cushion table Walls of the vessel Magnetic barriers Piston for the com- Magnetic piston pression of the gas Gas molecules Hover discs
How to proceed:
Align the air-cushion table horizontally and attach the magnetic barriers. Place the piston on the experiment surface right next to barrier no. 2. The guide piece for the magnetic piston placed onto magnetic barrier no. 2 ensures excellent guidance of the piston rod. Arrange the magnetic hover discs near barrier no.1. Turn the fan to a medium setting. Slowly move the piston towards barrier no.1 until the available area for the hover discs is less than half of the experiment surface. Observe the configuration and motions of the hover discs.
Result:
Reducing the area in size changes the behavior of the hover discs. The number of impacts in­creases. The distances in which the hover discs can move in a straight line become shorter and shorter. Oscillating and circular motions prevail. Permanent changes in location mostly occur as a mutual exchange of positions.
Interpretation:
Under certain conditions, the compression of a gas can result in liquefaction. The configuration of the molecules and their type of motion change in this process. While in the gaseous aggregati­on state only translational movements occur, the motion prevailing in the liquid state is oscillati­on around the respective location.
2.2.7 Solidification of a Liquid
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Hover disc, orange 25 Pieces
Model simulation
Real Object Model
Vessel containing Experiment surface of the liquid the air-cushion table Walls of the vessel Magnetic barriers Molecules of the Hover discs liquid
How to proceed:
Align the air-cushion table horizontally and attach
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the magnetic barriers. Spread the hover discs evenly across the experiment surface. Adjust the airflow strong enough to ensure that the hover discs lift off even when the impulse valve is opened. Briefly open the impulse valve several times so that the hover discs have a high mean kinetic energy. Observe the motions of the hover discs.
Result:
At first, the hover discs perform oscillating and circular motions superimposed on their translational movements. Their mean kinetic energy gradually drops. The amplitudes of the oscillations decrease, translational movements occur less often. After a while there still are
occasional exchanges of position. Finally, each hover disc only moves around its own equilibrium position.
Interpretation:
Reducing the temperature of a liquid leads to its solidification. The drop in temperature causes a drop in the mean kinetic energy of the molecules of the liquid. In the process of solidification, each molecule occupies a specific location, around which it performs irregular oscillating motions.
Note:
The mean velocity of the hover discs will drop faster when the fan is turned to a lower setting.
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2.3 Structure and Properties of Solids
2.3.1 Configuration and Motions of the Lattice Elements in a Solid
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Hover disc, orange 25 Pieces
Model simulation
Real object Model
Space in which the Experiment surface of behavior of the solid the air-cushion table is observed Adjacent lattice Magnetic barriers elements Lattice elements Hover discs
of the solid
How to proceed:
Align the air-cushion table horizontally, attach the magnetic barriers and spread the hover discs evenly across the experiment surface. Adjust the airflow strong enough so that the hover discs are sure to float even when the impulse valve is opened. Observe the motion of the hover discs after opening the impulse valve once.
Result:
Each hover disc is bound to a specific location. It performs oscillating and circular motions around its equilibrium position. The amplitudes vary and are constantly changing. The mean kinetic energy of the hover discs gradually decreases.
Interpretation:
The lattice elements in a solid are arranged in a regular configuration. They perform irregular oscillations around their equilibrium position. The amplitudes vary from location to location and change with time. A drop in temperature makes the mean kinetic energy of the oscillating lattice elements decrease.
Note:
To provide a proper demonstration of the drop in temperature it is recommended to turn the fan down as far as possible during the experiment. This experiment can also be demonstrated using red or green discs. It will be necessary, however, to reduce the effective experiment surface by shifting barrier no. 2 to the middle of the air­cushion table.
2.3.2 Melting a Solid
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Hover disc, orange 25 Pieces
Real object Model
Space in which the Experiment surface of behavior of the solid the air-cushion table is observed Adjacent lattice Magnetic barriers elements Lattice elements Hover discs
of the solid
Model simulation
How to proceed:
Align the air-cushion table horizontally and attach the magnetic barriers. Spread the hover discs evenly across the experiment surface. Adjust the airflow strong enough so that all hover discs are sure to float even when the impulse valve is opened. Open the impulse valve several times at an interval of several seconds and observe the motion of the hover discs.
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Result:
Initially, the hover discs are arranged regularly and perform oscillating and circular motions around their respective location. Then the amplitudes of their oscillations increase. Individual discs change their position. In the end, all discs temporarily perform translational movements in addition to the oscillations.Result: Initially, the hover discs are arranged regularly and perform oscillating and circular motions around their respective location. Then the amplitudes of their oscillations increase. Individual discs change their position. In the end, all discs temporarily perform translational movements in addition to the oscillations.
Interpretation:
A rise in temperature will make a solid body melt. While initially all lattice elements are bound to a fixed position around which they oscillate, there will be a subsequent superimposition of the os­cillations and translational movements.
Model simulation
Real object Model
Vessel containing Experiment surface of the gas the air-cushion table Walls of the vessel Magnetic barriers Piston in the vessel Magnetic piston
Gas molecules Hover discs
How to proceed:
Align the air-cushion table horizontally and attach the magnetic barriers. Place the piston close to barrier no. 2. Attaching the guide piece for the magnetic piston ensures excellent guidance of the piston rod. Place the hover discs on the experiment surface so that they are located near barrier no. 1. Turn up the fan so that all hover discs are sure to lift off. Shift the piston very slowly from barrier no. 2 towards barrier no. 1 until the piston has crossed the center of the experiment surface. Observe the motions of the hover discs.
2.3.3 Change of the Aggregation State of a Gas through Compression and Cooling
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Magnetic piston 1 Piece Guide piece for the 1 Piece magnetic piston Hover disc, red 21 pieces
Result:
At first, the hover discs perform the same motions as the molecules of a gas. The smaller the available area becomes, the stronger the impediment of the translational movements. In addition, there are oscillations of the hover discs around their respective location. The hover discs change their equilibrium position less often with time. Finally, each disc is located in a fixed position around which it performs oscillating and circular motions.
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Interpretation:
An increase in pressure and a drop in tempera­ture will transform a gas from the gaseous to the liquid aggregation state. While the molecules perform translational movements in the gaseous state, the prevailing motions in the liquid state are oscillations, superimposed by few transla­tions. In the solid state, the lattice elements are arranged in a regular configuration. They per­form oscillations around their equilibrium posi­tion.
2.3.4 Heat Conduction in Solids
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Hover disc, orange 25 Pieces
Model simulation
Real object Model
Space in which the Experiment surface of behavior of the solid the air-cushion table is observed Adjacent lattice Magnetic barriers elements Lattice elements Hover discs
of the solid
How to proceed:
Align the air-cushion table horizontally and attach the magnetic barriers. Spread the hover discs evenly across the experiment surface. Turn up the fan so that all hover discs are in
motion. Use one finger to set one of the hover discs located in a corner of the experiment surface into quick oscillating motions. (Take care to avoid damage to the experiment surface caused by friction.) Observe the motions of the hover discs.
Result:
The strong motion of the hover disc is gradually transferred onto the other ones.The strong motion of the hover disc is gradually transferred onto the other ones.
Interpretation:
Energy is transferred by heat conduction in sol­ids. A rise in temperature at one place of a solid will increase the mean kinetic energy of the lat­tice elements at that place. Due to the forces be­tween the lattice elements, the kinetic energy will be transferred to the adjacent elements. This caus­es the temperature to rise also in other places of the solid body.
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2.4. Processes of Electric Conduction
Physical Experiments on the Air-Cushion Table
2.4.1 Motion of an Electron in a Vacuum
Under the Influence of an Electric Field (Demonstrated By Means of Mechanical Forces)
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, short 1 Piece Hover disc, orange 1 Piece
Model simulation
Real Object Model
Space containing an Experiment surface of electric field the air-cushion table Strength of the Inclination of the electric field experiment surface Electron Hover disc
How to proceed:
Align the air-cushion table horizontally. Attach magnetic barrier no. 2 in a reversed position with the number facing downwards, in order to hold the hover disc. Use the adjusting screw at barrier no. 2 to lower the experiment surface on that side, selecting a slight inclination. Turn the fan to a medium setting. Place the hover disc on the opposite side of the experiment surface, holding it with the finger. Then release it and ob­serve its motion. Repeat the experiment selecting a stronger inclination of the experiment surface.
Result:
The motion of the hover disc accelerates. The ac­celeration increases with the degree of inclination.
Interpretation:
The motion of electrons in an electric field is ac­celerated, provided that no other forces act on the electrons. The acceleration increases with the intensity of the electric field.
2.4.2 Deflection of an Electron Radiation in the Electric Field
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, short 1 Piece Electrode 2 Pieces Manipulating rod 1 Piece Hover disc, green 2 Pieces Aluminum hover disc 5 Pieces High-voltage source
Model simulation
Real Object Model
Vacuum containing Experiment surface of an electric field the air-cushion table Electrodes Electrodes Electrons Aluminum hover discs
How to proceed:
Carefully align the air-cushion table in a hori­zontal position using the spirit levels. Place the electrodes onto the experiment surface parallel to sides nos. 1 and 2, so that the electrode on side no. 2 rests on its bases, while the bases of the other electrode point upwards. Position barrier no. 2 outside of the experiment surface on side no. 2, running parallel to the electrode on side no. 2. It is turned by 180° so that the hover discs cling to it because of the magnetic attraction.
Arrange 2 green hover discs closely to each other on side no. 3. They are meant to give the alumi­num disc a certain initial velocity. Feed the di­rect current of the high-voltage source to the elec­trodes. Use the manipulating rod to move an alu­minum disc towards the electrode on side no. 1, so that is charged. Then move it to the edge of the experiment surface on side no. 3, between the two green discs. Turn the fan to a medium setting and observe the motion of the hover disc. Repeat the experiment with the other aluminum discs, varying the distance of the green discs from the experiment surface.
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Result:
The hover discs move towards the opposite elec­trode on a parabolic path.
Interpretation:
Electrons are subject to a force in the electric field. When the electrons in a vacuum enter an electric field at a perpendicular angle to the field lines, they are forced onto parabolic paths. Their velocity increases in this process.
zontal position using the spirit levels. Arrange the electrodes at the edges of the experiment sur­face parallel to each other. The electrode on side no. 2 is set on its bases, whereas the bases of the other electrode point upwards. Place the magnetic barrier, turned by 180°, closely to the experiment surface parallel to the electrode on side no. 2, so that the hover discs cling to it due to the mag­netic attraction. Connect the electrodes to the high-voltage source in such way that the anode is located next to the magnetic barrier. Then place the hover discs onto the cathode. Feed d.c. voltage to the electrodes and turn the fan to a medium setting. Then lift the hover discs off the cathode using the tweezers and place them onto the experiment surface one by one, position­ing them directly in front of the cathode. Observe their motions between the electrodes.
Result:
The hover discs move from one electrode to the other in an accelerated way.
Note:
It is recommended to conduct this experiment with­out an electric field at first, in order to demonstrate the straight, uniform movement of the electrons.
2.4.3 Motion of Electrons in a Vacuum Under the Influence of an Electric Field
Components:
Air-cushion table with fan Overhead projector Electrode 2 Pieces Magnetic barrier, short 1 Piece Aluminum hover disc 5 Pieces Plastic tweezers 1 Piece High-voltage source
Model simulation
Real Object Model
Vacuum containing Experiment surface of an electric field the air-cushion table Electrodes Electrodes Electrons Hover discs made of
aluminum
How to proceed:
Carefully align the air-cushion table in a hori-
Interpretation:
The electrons in a vacuum will move in an accel­erated way from the cathode to the anode under the influence of an electric field.
2.4.4 Principle of Electric Conduction Components:
Air-cushion table with fan Overhead projector Electrode 2 Pieces Hover disc made of aluminum 5 Pieces Plastic tweezers 1 Piece High-voltage source
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Physical Experiments on the Air-Cushion Table
Model simulation
Real Object Model
Space containing an Experiment surface of electric field the air-cushion table Electrodes Electrodes Charge carriers Aluminum hover discs
How to proceed:
Align the air-cushion table horizontally. Arrange the two electrodes on two sides opposite each other, so that they rest directly on the experiment surface with their bases pointing upwards. Con­nect them to the high-voltage source. Place a hover disc directly next to an electrode. Feed d.c. voltage to the electrodes. Turn the fan to a setting in which the hover disc is sure to lift off. Then place the remaining discs onto the ex­periment surface one after the other, using the tweezers and placing them directly next to an elec­trode. Observe the motions of the hover discs.
Result:
The hover discs move back and forth between the electrodes under the influence of the electric field.
Notes:
This experiment offers a clear demonstration of the conditions existing for example when grains or aluminum flakes move back and forth between the plates of a plate capacitor through the influ­ence of the electric field. This setup is also suited to simulate the process of conduction with bipolar charge carriers. To do this, place an approx. 8-cm wide cardboard strip on each electrode. It should protrude from the electrodes approx. 3 cm into the space between the electrodes. When repeating the experiment under these conditions, the charge carrier seems to disappear in the respective electrode. Later it will leave the electrode as a “different” charge carrier (of the opposite polarity).
2.4.5 Influence of Lattice Elements on the Motions of Electrons in an Electric Field
Components:
Air-cushion table with fan Overhead projector Holding device Plexiglas plate Electrode 2 Pieces Manipulating rod 1 Piece Hover disc, orange 1 Piece Hover disc made of aluminum 4 Pieces High-voltage source
Interpretation:
When slightly moving particles (charge carriers) are located in an electric field, they will pick up charges at one electrode and transport them to the opposing one. There they will discharge these and pick up charges of the opposite polarity. Then they will return to the first electrode, etc. This directed movement of the charge carriers repre­sents a current.
Model simulation
Real Object Model
Part of a metallic Experiment surface of conductor the air-cushion table Lattice element Orange disc of the metal Electrodes Electrodes Conduction electrons Aluminum hover discs
How to proceed:
Align the air-cushion table horizontally. Arrange the two electrodes on two opposing sides of the experiment surface, so that they rest directly on its surface with their bases pointing upwards. Attach the holding device to the air-cushion table and insert the Plexiglas plate. Place the four alu­minum discs on the experiment surface and shift them towards one of the electrodes. Connect the electrodes to the high-voltage source. Feed d.c. voltage to the electrodes. Turn up the fan so that all hover discs lift off. Observe their
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motions. Then place the orange disc onto the Plexiglas plate above the center of the experi­ment surface. Its magnet should face downwards so that the aluminum discs are repelled. Set the Plexiglas plate to different heights to vary the influence of the orange disc on the aluminum ones. Observe their motions.
Result:
At first, the hover discs move from one electrode to the other and back. With the exception of few mutual interferences, these motions are mostly straight. The influence of the orange disc is a major im­pediment to these motions. The aluminum discs can often only succeed in reaching the opposite side after taking major detours. The lower the Plexiglas plate is set, the stronger the interfer­ence by the orange disc will be.
2.4.6 Motion of an Electron in a Metal Lattice Under the Influence of the Electric Field – Ohmic Resistance (Demonstrated By Means of Mechanical Forces)
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, short 1 Piece Holding device 1 Piece Lattice model 1 Piece Manipulating rod 1 Piece Hover disc, orange 1 Piece
Model simulation
Real Object Model
Part of a metallic Experiment surface of conductor the air-cushion table Metal lattice Lattice model Strength of the Inclination of the electric field experiment surface Electron Hover disc
Interpretation:
Conduction electrons move practically unimped­ed between the lattice elements of a metal. How­ever, near the lattice element there is strong in­terference.
Notes:
The fact that the directed movement of the elec­trons only occurs from the cathode to the anode is neglected intentionally.
How to proceed:
Align the air-cushion table horizontally. Turn magnetic barrier no. 2 by 180° and place it onto its position on the experiment surface. Attach the holding device to the air-cushion table and insert the lattice model. Slide it along the groove of the holding device until its edge at barrier no. 2 is positioned above the last row of holes in the air jet plate. This is to produce an approx. 3-cm wide strip between the lattice model and the pressure chamber through which the hover discs can be placed onto the experiment surface. Set the lat­tice model to the lowest position. Use the adjust­ing screw at barrier no. 2 to select a slight incli­nation of the table by lowering the table part at this side. Place the hover disc onto the experi­ment surface next to the pressure chamber. Turn up the fan to make the hover disc float. Ob­serve its motions and those of the hanging mag­nets. Repeat the experiment selecting different degrees of inclination for the experiment surface.
Result:
The lattice model influences the motions of the
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hover disc in such way that the mean drift veloc­ity is constant. The hover disc is slowed down by the interactions with the oscillating magnets. It transfers part of its energy to the magnets so that the amplitude of their oscillations increases. Both the velocity of the hover disc and the amplitude of the lattice oscillations increase as the degree of inclination of the air-cushion table is increased
range the magnetic barriers around the experi­ment surface. Attach the holding device to the air-cushion table and insert the lattice model. Set it to its highest position. Place the hover discs onto the experiment surface. Turn up the fan so that all hover discs move freely on the air-cushion table. Observe their motions and interactions with the magnets of the lattice model.
Result:
The motions of the hover discs are similar to those of the molecules of a gas. Interactions occur when they approach a magnet of the lattice model. A hover disc with a high velocity can make a hang­ing magnet oscillate at a higher amplitude. A hanging magnet with higher oscillations can cause the velocity of a hover disc to rise.
Interpretation:
The electrons in a metallic conductor move at a constant mean velocity under the influence of an electric field. In the course of interacting with the lattice elements they transfer part of their energy onto these, causing an increase in the lat­tice oscillations and therefore also a rise in the temperature of the conductor.
2.4.7 Motion of the Free Electrons in a Metal Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Holding device 1 Piece Lattice model 1 Piece Hover disc, red 25 Pieces
Model simulation
Real Object Model
Part of a metallic Experiment surface of conductor the air-cushion table Metal lattice Lattice model Electrons Hover discs
How to proceed:
Align the air-cushion table horizontally and ar-
Interpretation:
The motions of conduction electrons in a metal are similar to the motions of the molecules in a gas. They interact with the lattice elements. A rise in the temperature of the metal causes an increase in the mean velocity of the electrons. An increased velocity of the electrons causes a rise in the tem­perature of the metal.
2.4.8 Thermal Emission Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Holding device 1 Piece Lattice model 1 Piece Hover disc, red 15 Pieces Hover disc, green 11 Pieces
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Physical Experiments on the Air-Cushion Table
Model simulation
Real Object Model
Part of a metal Part of the experiment
surface under the dynamic lattice
Vacuum Part of the experiment
surface not situated under the dynamic
lattice Metal lattice Lattice model Electrons Hover discs
How to proceed:
Align the air-cushion table horizontally and ar­range the magnetic barriers. Attach the holding device and insert the lattice model. Set it to a medium height. Slide it outwards in the groove until 2 rows of the hanging magnets are located above the impulse valve. Attach one red disc to each hanging magnet of the remaining 3 rows. These cling to the magnets due to the magnetic attraction. Place the green discs on the experiment surface and slide them under the lattice model. Turn up the fan to a setting in which all discs are sure to lift off. Briefly open the impulse valve several times to increase the mean velocity of the hover discs and the amplitude of the hanging magnets. Observe the behavior of the hover discs.
Result:
Some of the hover discs overcome the forces of the lattice magnets and return to the vacant area of the air-cushion table. Some discs return to the space underneath the lattice model. The stronger the motions of the hover discs or lattice magnets, the more hover discs escape the space under the lattice model.
Interpretation:
To enable the electrons to escape the surface, they have to possess a specific minimum energy. This corresponds to the work of escape. Some of the electrons possess this kinetic energy at high tem­peratures of the metal. The higher this tempera­ture is, the more electrons can escape it in a spe­cific period of time.
2.4.9 Bound Charge Carriers in an Insulator
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Holding device 1 Piece Lattice model 1 Piece Manipulating rod 1 Piece Hover disc, red 25 Pieces
Model simulation
Real Object Model
Part of an insulator Experiment surface of
the air-cushion table Crystal lattice of Lattice model the insulator Strength of the Inclination of the electric field experiment surface Electrons Hover discs
How to proceed:
Align the air-cushion table horizontally and at­tach the magnetic barriers. Spread the 25 hover discs evenly across the experiment surface. Then attach the holding device and insert the lattice model. Set it to the lowest possible height, tak­ing care, however, that the hover discs are not attracted by the hanging magnets. Turn the fan to a setting in which all hover discs lift off. Observe their motions and interactions with the lattice model. Then gradually increase the degree of inclination of the experiment sur­face and observe the behavior of the hover discs.
Result:
All hover discs are tightly bound to their loca­tion and oscillate around their equilibrium posi­tion at low amplitudes. Even when the experi­ment surface is inclined to a higher degree, they will not escape their positions.
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Interpretation:
In an insulator, the electrons are bound tightly to the atomic nuclei. They cannot escape their posi­tions even under the influence of an electric field.
Physical Experiments on the Air-Cushion Table
Position the orange disc in a corner of the ex­periment surface and hold it with the finger at first. Then release it and observe the changes caused by this hover disc.
Result:
The orange disc moves across the experiment surface in a disorderly fashion, driving some of the red discs from their positions. These discs then move between the other bound discs as well, but return to fixed positions after a certain pe­riod of time.
2.4.10 Behavior of a Free Charge Carrier in an Insulator
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Holding device 1 Piece Lattice model 1 Piece Manipulating rod 1 Piece Hover disc, red 25 Pieces Hover disc, orange 1 Piece
Model simulation
Real Object Model
Part of an insulator Experiment surface of the air-cushion table Crystal lattice of Lattice model the insulator Bound electrons Hover discs, red Bombarding Hover disc, orange charge carrier
How to proceed:
Align the air-cushion table horizontally and at­tach the magnetic barriers. Spread the red discs evenly across the experiment surface. Attach the holding device to the air-cushion table and insert the lattice model. It should be positioned closely above the experiment surface. Turn up the fan to a setting in which all discs are sure to lift off. One red disc should be positioned under each hanging magnet. If necessary, use the manipulating rod to ensure this arrangement.
Interpretation:
Bombarding an insulator with a fast charge car­rier causes the release of some electrons under its influence. These can migrate for a certain period of time, allowing a current to flow in an insulator. This is the case e.g. when specific non­conductors are exposed to high-energy radiation.
Note:
The effect can be enhanced by removing the red disc, which would be first hit by the orange disc.
2.4.11 Electric Conduction in a Semiconductor – Intrinsic Conduction (Demonstrated By Means of Mechanical Forces)
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Holding device 1 Piece Lattice model 1 Piece Manipulating rod 1 Piece Hover disc, red 25 Pieces
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Physical Experiments on the Air-Cushion Table
Model simulation
Real Object Model
Part of a Experiment surface of semiconductor the air-cushion table Crystal lattice of Lattice model the semiconductor Positive ions of the Lattice magnets crystal lattice Electrons Hover discs
How to proceed:
Align the air-cushion table horizontally and at­tach the magnetic barriers. Spread the discs evenly across the experiment surface. Attach the holding device to the air-cushion table and insert the lattice model. Set it to a medium height. Turn the fan to a setting in which all discs are sure to lift off. If necessary, use the manipulating rod to ensure that there is a disc under each hang­ing magnet. Repeatedly open the impulse valve to increase the velocity of the hover discs. Ob­serve their configuration and motions. Finally, gradually increase the degree of inclina­tion of the table using the adjusting screw at bar­rier no. 2 and observe the influence of the degree of inclination on the hover discs.
Result:
At low velocities, all hover discs are positioned under the magnets of the lattice model. At higher velocities, some of the hover discs leave their positions. The effect of inclining the experiment surface is that the disordered motions of the hover discs receive a preferential direction.
rise in temperature, so that they move through­out the semiconductor. The released electrons leave behind positive “holes”. The number of migrating electrons and the number of holes are equal. Feeding voltage causes an electric cur­rent to flow. The preferential motion of the elec­trons is towards the positive electrode, that of the “holes”, as it seems, in the opposite direction.
2.4.12 Electric Conduction in a Semiconductor – N-Type Conduction (Demonstrated By Means of Mechanical Forces)
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Holding device 1 Piece Lattice model 1 Piece Manipulating rod 1 Piece Hover disc, red 28 Pieces
Model simulation
Real Object Model
Part of a semi- Experiment surface of conductor the air-cushion table Crystal lattice of Lattice model the semiconductor Positive ions of Lattice magnets the crystal lattice Electrons Hover discs Strength of the Inclination of the electric field experiment surface
Interpretation:
In an intrinsic semiconductor, some electrons are released from the lattice under the influence of a
How to proceed:
Align the air-cushion table horizontally and at­tach the magnetic barriers around the experiment surface. Spread the discs evenly across the ex­periment surface. Attach the holding device and insert the lattice model. Set it to a medium height. Turn the fan to a setting in which all hover discs float freely. Observe the configuration and mo­tions of the hover discs. Then tilt the experiment surface of the air-cushion table. Open the impulse valve several times and repeat the experiment at an increased velocity of the hover discs.
Result:
At the lower velocity, 25 hover discs are bound rather closely to the magnets of the lattice model. The other three move in the gaps between them in disorderly fashion. The effect of inclining the
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Physical Experiments on the Air-Cushion Table
experiment surface is that the disordered motions of the hover discs are superimposed by directional movements. An increase in velocity also causes some of the bound discs to leave their positions.
Interpretation:
In a semiconductor with N-type conduction, mi­grating electrons are found even at low tempera­tures. Feeding voltage causes a current to flow, this current being produced by these electrons. At higher temperatures, further electrons are re­leased for the charge transport.
How to proceed:
Align the air-cushion table horizontally and at­tach the magnetic barriers. Spread the 22 discs evenly across the experiment surface, attach the holding device and insert the lattice model. Set it to a medium height. Turn the fan to a setting in which the discs are sure to lift off. Then tilt the experiment surface. Observe the configuration and motions of the hover discs. Repeat the experiment at an increased velocity of the hover discs.
Result:
The hover discs are bound to the magnets of the lattice model. Some positions, however, remain vacant. As adjacent discs change over into va­cant positions, the “holes” move. The inclination of the experiment surface causes a superimposi­tion of a directional movement.
2.4.13 Electric Conduction in a Semiconductor – P-Type Conduction (Demonstrated By Means of Mechanical Forces)
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Holding device 1 Piece Lattice model 1 Piece Manipulating rod 1 Piece Hover disc, red 22 Pieces
Model simulation
Real Object Model
Part of a semi- Experiment surface of conductor the air-cushion table Crystal lattice of the Lattice model semiconductor Positive ions of the Lattice magnets semiconductor Electrons Hover discs Strength of the Inclination of the electric field experiment surface
Interpretation:
In a semiconductor with p-type conduction some locations within the lattice are not occupied by electrons. These “holes” are often filled up by adjacent electrons, creating new “holes.” When feeding a voltage, the positive “holes” move in the direction of the negative electrode. At higher temperatures, additional “holes” are created.
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2.5 Nuclear Physics
Physical Experiments on the Air-Cushion Table
2.5.1 Scattering of Positively Charged Particles Near an Atomic Nucleus
Components:
Air-cushion table with fan Overhead projector Holding device Plexiglas plate Hover disc, orange 5 Pieces
Model simulation:
Real Object Model
Space in which the Experiment surface of positively charged the air-cushion table particles move Atomic nucleus Stacked hover discs Positively Hover disc charged particle
How to proceed:
Carefully align the air-cushion table to a hori­zontal setting using the spirit levels. Attach the holding device to the air-cushion device and in­sert the Plexiglas plate. Place the 4 stacked discs in the middle of the Plexiglas plate with their magnets facing down­wards. This is to ensure repulsion of the hover disc on the experiment surface. Set this disc into motion at the lowest possible velocity from the edge of the experiment surface towards the stacked magnets. Repeat this experiment at various speeds. Then vary the direction of motion, making the hover disc float along the stacked magnets at gradually increasing distances from experiment to experi­ment.
Result:
The hover disc changes its direction of motion near the stacked magnets. This change in the di­rection of motion is stronger the lower the veloc­ity of the hover disc is and the closer the path runs along the stacked discs.
Interpretation:
Charged particles are scattered near the atomic nucleus. The scattering angle depends on the velocity and the initial direction of the particles.
2.5.2 Scattering of Alpha Particles When Passing Through a Metal Foil
Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Magnetic barrier consisting 1 Piece of 4 magnets Hover disc, red 1 Piece
Model simulation:
Real Object Model
Space in which the Experiment surface of alpha particles move the air-cushion table Metal foil Magnetic barrier made
of 4 magnets Atomic nuclei Ceramic magnets of the barrier Alpha particles Hover discs
How to proceed:
Carefully align the air-cushion table to a hori­zontal setting using the spirit levels. Attach the magnetic barriers, turning barrier no. 2 by 180° so that it holds the approaching hover disc. Place the ends of the magnetic barrier consisting of 4 magnets into the recesses provided in barriers no. 3 and 4 which are located near barrier no. 2. Turn the fan to a setting in which the hover disc floats freely. Move it closely to barrier no. 1. Hold it with the finger at first, then suddenly release it so that it hits the barrier of 4 magnets at high velocity. Repeat the experiment with slight variations of the starting position. Observe the motion of the hover disc through the magnetic barrier.
Result:
In most cases, the hover disc will pass through
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the magnetic barrier with the ceramic magnets without any noticeable deflection. In various cases it will change its direction of motion. It will rebound only in very rare cases.
Interpretation:
In Rutherford’s scattering experiment almost all alpha particles traverse the metal foil. Only a few of them are deflected from their original direction. Strong dispersion occurs only in very rare cases.
How to proceed:
Align the air-cushion table horizontally. Attach the magnetic barriers and the holding device to the air-cushion table. Insert the Plexiglas plate and position it closely above the experiment sur­face. Place the orange disc in the middle of the Plexiglas plate. Turn the fan to a setting in which the red disc is sure to lift off. Use the manipulating rod to move it under the orange disc on the experiment sur­face. Observe its motions. Then increase its ve­locity by hitting it with the manipulating rod and observe it again.
Result:
The red disc moves around the orange one on varying paths. The parameters of the paths de­pend greatly on the speed.
Note:
The influence of the magnetic barrier on the mo­tion of the hover discs can be varied by placing the barrier on the Plexiglas plate and setting the plate to the desired height. The effect of the bar­rier is enhanced by placing orange discs on the ceramic magnets.
2.5.3 The Rutherford Atomic Model Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Holding device 1 Piece Plexiglas plate 1 Piece Manipulating rod 1 Piece Hover disc, orange 1 Piece Hover disc, red 1 Piece
Model simulation:
Real Object Model
Atom Experiment surface of
the air-cushion table Atomic nucleus Hover disc, orange Electron Hover disc, red
Interpretation:
These experiments provide simply illustrated con­cept of the structure of an atom. They offer a viv­id demonstration of the Rutherford atomic mod­el, which was developed based on the results of the scattering experiments.
Note:
The experiment can be varied by stacking sev­eral orange discs and adjusting the height of the Plexiglas plate accordingly.
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2.6 Mechanical Motions
2.6.1 Vertical, Horizontal and Diagonal Projection
Components:
Air-cushion table with fan Overhead projector Hover disc, orange 2 Pieces
Model simulation:
Real Object Model
Space in which the Experiment surface of projection takes place the air-cushion table Influence of the Force resulting from gravitational field slight inclination of the
experiment surface
Projectile Hover disc
How to proceed:
Align the air-cushion table horizontally, place the disc in the middle of the surface and turn up the fan until the disc is sure to float. Then tilt the experiment surface slightly using the adjusting screw on side no. 4. Hold the disc at the upper edge with the pointer and then release it without providing an initial motion. The projected image should clearly show the acceleration of its mo­tion. The motion should not be too fast (by se­lecting an appropriate degree of inclination!). After this preliminary experiment (model experi­ment on the free fall), it is possible to demon­strate the various trajectories of projection. It will be necessary to select suitable starting points and an appropriate starting speed adapted to the “fall time” determined in the preliminary experiment.
Physical Experiments on the Air-Cushion Table
ble to demonstrate motions at very low speed.
2.6.2 Elastic Collision Components:
Air-cushion table with fan Overhead projector Magnetic barrier, long 2 Pieces Magnetic barrier, short 2 Pieces Hover disc, orange 4 Pieces
Model simulation:
Real Object Model
Surface on which the Experiment surface of colliding objects move the air-cushion table Objects participating Hover discs in the elastic collision
Type of projection Starting point
vertically upwards middle of side no. 3 horizontal top of side no. 2 diagonal bottom of side no. 2
Result:
The paths correspond to the flight paths in the vertical, horizontal and angular projection of an object.
Interpretation:
Since the experiment surface is tilted, uniform motions and motions with regular acceleration are superimposed, producing motions which cor­respond to those occurring in projections. The slight inclination of the experimenting surface causes only slight acceleration, making it possi-
How to proceed:
Carefully align the air-cushion table horizontally using the spirit levels and attach the magnetic barriers. Place two stacked hover discs in the middle of the experiment surface. Place the other doubled disc in a corner of the experiment surface, holding it with the finger and then releasing it so that it approaches the first. Repeat this process several times, with stronger or lesser deviations from a central collision. Observe the motion of both discs before and after the collision.
Result:
In case of a central collision both discs (with equal mass) exchange their velocity and therefore their kinetic energy. If the collision is not central, only part of the energy will be transferred.
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Interpretation:
The air-cushion principle and utilization of the magnetic repulsive forces between ceramic magnets allow for demonstrations of fully elastic collisions.
Turn the fan to a medium setting. Set two stacked discs into slow motion starting from the edge of the experiment surface. Select a direction ensuring that it will float along the stacked discs at a distance of a few centimeters. Repeat the experiment several times, gradually reducing the shortest distance between the moving and the stacked discs. Observe the motion of the hover discs.
Result:
The hover disc will move in a straight and uni­form way as long as there is no force acting on it. Its direction of movement changes near the stacked discs. The shorter the distance to the stacked discs, the stronger the change in direction.
Note:
Collisions of objects with different masses can be demonstrated by using a doubled orange disc as one collision partner and a single disc as the other.
2.6.3 Change in the Direction of Motion of an Object with a Force
Components:
Air-cushion table with fan Overhead projector Holding device Plexiglas plate Manipulating rod Hover disc, orange 6 Pieces
Model simulation:
Real Object Model
Surface on which the Experiment surface of object moves the air-cushion table Object subject to Orange disc a force Center of force Stacked discs
How to proceed:
Align the air-cushion table horizontally, attach the holding device and insert the Plexiglas plate. Stack four discs on the Plexiglas plate in the middle of the experiment surface.
Interpretation:
When a moving object is subjected to a force, it will be accelerated. If the direction of the force is perpendicular to the motion, the speed remains unchanged, but the direction of motion changes. The greater the force, the stronger the change in direction.
CONCLUDING REMARKS
The preceding chapters provide an overview of the setup, operating mode and possible uses of the air-cushion table. Approximately 50 experiments are described, including specific physical annotations, as well as notes on the laboratory practice of the experiments and their didactic methodology. The following remarks are intended to complete and conclude the instructions for conducting the experiments:
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Physical Experiments on the Air-Cushion Table
The instructions provide an overview of the main uses of the air-cushion table. The se­lection and configuration of the experiments used for teaching purposes shall be deter­mined by the instructor.
The physical interpretation of each experi­ment is given on a simple level, in accordance with the usually rough model illustration.
The air-cushion table is a suitable teaching aid from the high school to the university level. The selection of the described experi­ments and the way of conducting them is meant to be exemplary.
Although the air-cushion table was created for demonstration experiments, it is also suited for lab experiments, especially of the
quantitative type.
All described experiments can be demon­strated in a convincing way if they are opti­mized on the basis of these instructions. Following the instructions literally does not guarantee convincing effects.
The air-cushion table is a high-quality prod­uct, which should be handled with care. Cleanliness, knowledge and skill are neces­sary for its successful usage.
Taking all of these remarks into consideration, the air-cushion table is highly effective teaching aid which will make a major contribution to a more profound understanding of physical phenomena , processes, terms and laws.
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