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Instruction Manual and
Experiment Guide for
the SE-8747
Kinesthetics Cart
KINESTHESIA-1
A One-Dimensional Kinesthetic Apparatus to Teach Mechanics
012-05787C
3/96
© 1995 Hans Pfister, Dickinson College $10.00
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T able of Contents
Section Page
Warranty, and Equipment Return ......................................................................ii
Introduction ......................................................................................................1
Equipment ........................................................................................................2
General Operation and Safety Precautions .........................................................3
Experiments:
Experiment 1: Newton’s First Law ..............................................................4
Experiment 2: A Special Case of Newton’s First Law..................................6
Experiment 3: Newton’s Second Law: The Human Slingshot ......................7
Experiment 4: Newton’s Second Law: The Bucket Accelerator ...................8
Experiment 5: Eradicating the Coin-Toss Misconception............................. 9
Experiment 6a: Independence of the X and Y Motion of a Projectile...........10
Experiment 6b: Independence of the X and Y Motion of a Projectile .......... 11
Experiment 7: Motion in 2-D: Uniform Motion vs. Accelerated Motion ..... 12
Experiment 8: Newton’s First Law .............................................................13
Experiment 9: Center of Mass / Conservation of Momentum ......................14
Experiment 10: The Simple Harmonic Oscillator........................................15
Experiment 11: The Human Oscilloscope...................................................15
Additional Experiments Possible with the Collision Attachment .......................16
Experiment 12: Newton’s Third Law: A Crashing Experience.................... 17
Experiment 13: Newton’s Third Law Misconception.................................. 18
Experiment 14: Another Newton’s Third Law Misconception .................... 18
Experiment 15: And another Newton’s Third Law Misconception .............. 19
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Warranty and Equipment Return
Limited Warranty and Equipment Return
This product is warranted to be free from defects in
materials and workmanship for a period of one year from
the date of shipment to the customer.
Should you experience any problems with the equipment,
please contact PASCO scientific.
Address: PASCO scientific
10101 Foothills Blvd.
P.O. Box 619011
Roseville, CA 95678-9011
Phone: (916) 786-3800
FAX: (916) 786-8905
email: techsupp@PASCO.com
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Introduction
The sensory experience that is “mediated by end organs
located in muscles, tendons, and joints and stimulated by
bodily movements and tensions is known as Kinesthesia
or Kinesthesis” 1 –derived from the Greek words kinein
(to move) and aisthesis (perception). There is good evidence that in certain contexts kinesthetic experience can
be more engaging and memorable than many other learning experiences.
For example, video arcades feature games that incorporate the entire body of the player into their video adventures. One player for example mounts a replica of a
Yamaha 750 and grips a mock handle bar as artificial
countryside and pieces of road pass in front of the cycle
on a 50” high screen. As the player turns the handle bars
the motorbike tilts through an angle to provide the player
with a kinesthetic experience of turning. An actor memorizing a script commonly recites lines aloud and uses
muscle memory to aid learning.
Many articles have been published to date that indicate
the importance of kinesthetic experiences in the learning process and show how powerful they are in helping students to relate natural phenomena to the laws of
mechanics.
Seven years ago, the Physics Department of Dickinson
College converted their introductory physics courses into
a workshop format that places the experiments in the
hand of the students and affords them the possibility of
rediscovering fundamental laws of physics. More recently, we have started to introduce a series of kinesthetic
apparatus into our curriculum. This carries the Workshop
Physics idea even further: Instead of letting the students
perform the experiment, we now physically incorporate
students into the experiment. Several kinesthetic activities
have in the meantime been tested in the Workshop Physics program. They also prove to be effective in more conventional lecture and laboratory settings.
Furthermore, kinesthetic experiences are helpful in eliminating some of the traditional student conceptions. Students usually have derived these non-Newtonian “common sense conceptions” from everyday experiences. Of
course, the reason that these conceptions are non-Newtonian
comes from the fact that practically all motions we encounter
in our everyday life involve friction in one form or another.
One such student-conception is that one must apply a constant force to produce motion at a constant velocity.
Finally, kinesthetic experiences are also highly motivating. Students enjoy riding on these kinesthetic carts and
delight in the experience which is retained as a muscle
memory.
The SF-8747 Kinesthetics Cart, a.k.a. Kinesthesia-1, affords students the opportunity to experience Newton’s
laws kinesthetically. Students can experience motions associated with various forces including constant velocity,
constant acceleration and collisions. It also helps to eradicate some common misconceptions of beginning physics
students. This manual lists a series of experiments and
demonstrations that are possible with Kinesthesia-1. It
also provides examples of how Kinesthesia-1 can be used
to help enhance student understanding of both quantitative and qualitative aspects of Newton’s Laws.
➤ WARNING!
For all of the experiments and
demonstrations involving Kinesthesia-1 with the exception of Experiment 10, it is of paramount
importance that at no time a student should stand on the device!
1
Webster’s College Dictionary.
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Equipment
The following is a description of the equipment that is
included with the SE-8747 Kinesthetics Cart:
• Lower cart of the Kinesthetics Cart
• Upper cart or the Kinesthetics Cart
• (1) Coupler
• Manual
Required for some experiments but not supplied:
• a block of 4”x4”x2” of wood that is to be screwed to
the floor for one of the experiments illustrating
Newton’s First Law.
• SE-8748 Collision Attachment (2 required for collision experiments)
Please refer to each experiment to determine all the necessary equipment
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General Operation and Safety Precautions
The SE-8747 Kinesthetics Cart system consists of two
low friction carts that move along a straight line. Both
carts are supported by roller blade wheels. The two carts
are designed to ride “piggy-back-style” on top of each
other. Throughout this manual we will refer to the two
carts as the “lower cart” (this is the narrower cart) and the
“upper cart” (this is the wider cart). The two carts can be
interlocked or ridden separately. To interlock the two
carts, the upper cart is placed on top of the lower cart
so that the coupler holes of each cart line up. Then the
coupler is inserted through the two bores in the upper
cart into the two bores of the lower cart.
As long as the upper cart rides on top of the lower cart the
roller blade wheels of the upper cart are approximately
1/8” to 1/4” off the floor. The wheels of the upper cart
serve in this application as “landing gear” (e.g. Experiments 1 and 2).
For any experiment that requires removal of the coupler
during the experiment, it is advisable to have the student
rider try out its function prior to the experiment. Have the
student remove the coupler and insert it back through the
bores of the upper cart into the coupler holes of the lower
cart. The coupler is removed most easily by pulling it up
as vertically as possible.
Most experiments and demonstrations involving Kinesthesia-1 can be done in both qualitative and quantitative
fashions. The motion (distance, velocity and acceleration)
of the Kinesthetics Cart can be inferred with standard Microcomputer Based Lab (MBL) apparatus. The position
can be recorded with either a motion detector or with
PASCO’s Smart Pulley. In the latter case, a sufficiently
long string is wrapped around the pulley which is stationary near a computer. The free end of the string is attached
to the back of the moving Kinesthetics Cart. Also, a standard accelerometer can be readily mounted on the cart.
All experiments and demonstrations with the Kinesthetics
Cart involve little or virtually no setup time.
➤
IMPORTANT!
STORE THE KINETHETICS CART IN A VERTICAL POSITION WITH THE WHEELS UP.
IF THE UNIT IS STORED SITTING ON ITS
WHEELS, THEY MAY DEVELOP A FLAT
SPOT.
➤
CAUTION!
WHENEVER YOU PERFORM AN EXPERIMENT DESCRIBED IN THIS MANUAL OR TRY
OUT NEW EXPERIMENTS INVOLVING THE
KINESTHETICS CART, BE SURE TO ELIMINATE ANY RISK OF POSSIBLE INJURY!
• While the cart is in motion at least one
hand of the student rider must maintain a firm grip on the handle or hold
on to the cart itself. (Except for Experiment 10)
• It is highly recommended that the student rider wear a bicycle helmet while
riding the cart.
• AT NO TIME MAY A STUDENT RIDER
STAND ON THE UPPER OR LOWER
CART! (Except for Experiment 10)
When performing Experiment 10 it is imperative that all necessary precautions be
observed to keep a student from injury:
• line both sides of the cart’s path with
foam mats
• place spotters along the cart’s path
to support the student’s ascent and
descent.
FOR COLLISION EXPERIMENTS: Student
must have feet against collision attachment
for additional support of the body. Student
body might move forward toward front of
cart. For this experiment it is particularly important to hold on to the cart with both
hands. Keep body in as rigid a position as
possible.
• Only one rider should be on the cart when
riding “piggy-back-style”.
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Experiment 1: Newton’s First
Most often we find Newton’s First Law paraphrased in a form like this: “A body will remain in its
state of motion unless acted upon by an external force.” We can paraphrase it even a little more to
accentuate the essence of the First Law for our students and word it something like this: “A body
moving at constant velocity vc will keep moving at this constant velocity vc, no matter what happens to the world around this body, unless acted upon by an external force.” This of course contradicts our everyday experience: our car will not keep moving at a constant 55 mph unless we keep
applying a steady force. Here, Kinesthesia-1 affords a unique opportunity for students to experience in the classroom that Newton is correct indeed.
At the center of the classroom (or any other convenient location of the lecture hall) a short
section (approx. 4”) of a two-by-four is attached to the floor. A student rider initially has both carts
coupled together and is accelerated to an initial velocity v
student rider has attained the constant velocity vc, (s)he separates the two carts by pulling the coupler straight up. Now, the student rider and the upper cart ride quasi friction-free, piggy-back-style
on top of the lower cart, approaching the two-by-four block in the center of the classroom. A few
seconds later, the worst case scenario happens. The two-by-four block abruptly stops the lower
cart, i.e., the world underneath our rider comes to a complete stop. But what will happen to the
upper cart and the rider? If Newton is right, the upper cart and the rider will, contrary to our everyday experience, continue to move at a constant velocity vc, since there is no force acting on them.
Indeed, this is what our rider experiences. As the top cart and the rider keep moving beyond the
limit of the lower cart, the “landing gear” (roller blade wheels on the upper cart) ensures a fairly
smooth landing. This kinesthetic experience not only verifies Newton’s First Law but with the
small jolt of the touchdown the First Law is ingrained in the students’ memory and will be remembered for a long time past this experience.
by his or her partner. As soon as the
c
Figure 1.1: A student rider is given a constant velocity vc by her partner. The upper and lower cart are
coupled together.
Figure 1.2: The student rider removes the coupler
as she approaches the 4”x4”x2” block mounted to
the floor.
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Figure 1.3: The lower cart is being abruptly stopped
by the 4”x4”x2” block. However, the student rider
and the upper cart continue to move with constant
velocity vc.
For the success of this experiment it is important to align the Kinesthetics Cart precisely, so that
the 4”x4”x2” block mounted to the floor meets the middle of the bumper of the lower cart. Misalignment to a degree that a wheel will hit the 4”x4”x2” block, might result in damage to the
Cart and possible injury to the rider.
This past semester, one of my students participated in the experiment described above in
Experiment 1 where she was riding on Kinesthesia-1 at constant velocity v while the lower cart
got abruptly stopped. Two weeks later she remembered her kinesthetic classroom experience
while working in the kitchen of the student dining hall. She was pushing a cart loaded with a
large stack of trays when suddenly the front wheels of her cart got stuck at a ridge in the floor.
As the trays went flying she exclaimed with excitement: “Newton’s First Law!!”
What a nice testimony, evidencing the fact that kinesthetic experiences facilitate the transfer
of lessons encountered in the classroom to the “world out there”.
Figure 1.4: The student and the upper cart continue
to move with constant velocity vo in accordance with
Newton’s First Law, while the lower cart has come to
a complete stop.
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Experiment 2: A Special Case of Newton’ s First Law
Kinesthesia-1 is also perfectly suited to illustrate the vo= 0 m/s case of Newton’s First Law.
Here again, we paraphrase Newton’s First Law to get the decisive point across: “A body at rest
will remain at rest unless there is an external force acting on it!” Or even more pronounced: “A
body at rest will remain at rest no matter what happens to the world around it, as long as there is
no external force acting on it.” To illustrate this special case of Newton’s First Law, a student is
sitting in anticipation on the decoupled Kinesthesia-1 cart as illustrated in Fig. 2-1. The instructor, holding the rope that is tied to the lower cart, solicits a prediction from the student and the
rest of the class. If Newton is right, the student rider should not move. As the instructor accelerates the lower cart out from underneath the student the upper cart lands gently on the landing
gear. With this gentle impact this special case of Newton’s First Law is imprinted into the students’ brain. We would like to note that this experiment works better than the traditional demonstration of the table cloth trick since the inertia of a student is in general larger than the inertia of
a dinner plate.
Figure 2-1: A student rider sits on the decoupled
Kinesthetics Cart awaiting for some drastic event to
happen. Then the “world” underneath begins to
move suddenly when a second student pulls on the
rope which is attached to the lower cart.
Figure 2-2: The student rider and the upper cart
having no force acting upon them remain at rest as
the lower cart is pulled out from underneath. The
roller blade wheels of the upper cart (the “landing
gear”) are designed such that the student rider and
upper cart drop only a very small distance.
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Experiment 3: Newton’s Second Law
“The Human Slingshot”
For a qualitative illustration of Newton’s Second Law we suggest the following demonstration
requiring virtually no setup time. This demonstration is especially valuable if student insight into
Newton’s Second Law is desired in the basic form of:
“...the larger the mass - the smaller the resulting acceleration....”
A student volunteer rides on the Kinesthetics Cart. Four strands of 10 m long bungee cords
are placed around the back of the student rider. The ends of the bungee cords can either be held
in place by several student assistants or be attached to appropriate wall or floor mounting. The
cart and student rider are pulled back to a suitable location marked on the floor and released.
Then the experiment is repeated with the most massive and least massive student in the class.
➤ NOTE: For small classrooms it is recommended that several students are suitably positioned
to catch the student rider before (s)he collides with a wall or other object in the room. A bungee
cord catch mechanism is also conceivable.
Figure 3-1: A student holds on to the Kinesthetics
Cart while she is being pulled back to a fixed position marked on the floor. The four strands of bungee
cord are simply placed around her back.
The fact that the accelerating force is not constant in this particular experiment does not
seem to create much problem with most students. However, if students object, the bungee cords
can simply be replaced by the constant tension apparatus (e.g. “bucket accelerator” in Experiment 4).
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Experiment 4: Newton’s Second Law
“The Bucket Accelerator”
For a quantitative verification of Newton’s Second Law we recommend the use of a “Bucket
Accelerator”. A student of mass ms is riding on the Kinesthetics Cart of mass mc. The student
and cart experience a constant acceleration due to the constant tension force FT in the rope. (One
might want to return to this same setup when the Atwoods machine is being discussed.)
If there is sufficient ceiling height two pulleys will suffice. Otherwise a double pulley sys-
tem like the one shown in Fig. 4-1 can be used.
Fig. 4-1: A student and the Kinesthetics Cart of combined mass ms+mc is being accelerated by a constant
tension force FT. The accelerating tension force is being
modified by changing the number of weights in the
bucket. The acceleration of the student and the cart is
determined with a motion detector.
➤ CAUTION!
Keep clear of the area beneath
the bucket at all times!
For a quantitative verification of Newton’s Second Law, we like to accelerate the cart and
student rider over a distance of a few meters. If a lecture hall is available with a sufficiently high
ceiling, this can be done simply with two pulleys: one mounted to the wall a few inches off the
floor, and the second one securely mounted at a suitable location on the ceiling. For classrooms
with a low ceiling or no ceiling access, one can build a simple rack and use an arrangement of
two double pulleys such that a 2 m drop of the bucket results in 8 m of travel for the cart. Although pulleys are available at minimal cost at a hardware store, for quantitative measurements it
is recommended to use some heavy-duty custom-made pulleys containing high quality ball bearings. A motion detector tracks the student on the cart and a computer monitor displays diagrams
of x(t), v(t), and a(t) while the student is undergoing the motion. The constant tension in the
string is monitored with a force probe. The dependence of the acceleration on the tension in the
string, i.e., the accelerating force, is obtained by varying the number of mass pieces in the bucket;
the dependence of the acceleration on the mass is obtained by using a number of different
masses. Finally, all relevant data is transferred to a spreadsheet and disseminated to the rest of the
class for evaluation.
We would like to note that the setup time for our “bucket accelerator” is comparable to the
setup time for an air track. As a precaution, it is imperative that everyone keeps clear of the area
beneath the bucket. One can place some rubber sheets and/or some foam rubber in the area beneath the bucket.
Although there are no real advantages to this particular way of verifying Newton’s Second
Law it is certainly more fun for the students to be a part of the experiment.
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Experiment 5: Eradicating the
Coin T oss Misconception
One student conception we inevitably encounter in an introductory
physics course is known as the “Coin Toss Misconception”. A coin is
tossed vertically up into the air. The question is: “What is the force on
the coin after it has left the hand (a) on its way up, (b) at the turnaround point, and (c) on its way down.” A standardized test that has
been given to over a thousand students over the past few years shows
that a great majority of all students answer part (a) of this question to
the effect that there is a force in the direction of motion, i.e., in the
upward direction. Certainly, there are many remedies to correct this
student conception. However, this can be done very effectively
through an unforgettable kinesthetic experience.
A student rides on Kinesthesia-1 and is asked to hold on to the constant tension rope of the
“bucket accelerator” introduced in Experiment 4. A force probe is inserted between rope and
hand so that the student can give us many force readings during the entire experiment. Now we
explain to the class that it is impractical to toss a student up into the air to determine the forces
acting on that individual. Therefore, we tilt the coin-toss experiment through a 90
vertical to horizontal and now the student sitting on Kinesthesia-1 plays the role of the coin,
while the constant tension rope takes on the role of the gravitational force.
°
angle from
Fig. 5-2. One of the most common student conception, known as the coin toss misconception,
can effectively be corrected using Kinesthesia-1. The experiment is brought from the vertical to
the horizontal. Gravity is replaced by the constant tension apparatus of Experiment 4. The student is given an initial push in the “UP” direction (i.e. away from the constant tension apparatus).
The student verifies and reports to the class that the force is constant and in the “DOWN” direction at all times. In particular, the force is “DOWNWARD” on the way “UP”, “DOWNWARD” in the
turnaround point, and “DOWNWARD” on the way “DOWN”.
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The equivalence of the two different motions is easily shown by comparing the motion detec-
tor traces of a coin toss with those of the horizontally moving cart.
If only a qualitative answer is desired this experiment can be simplified by having the student
rider simply hold on to one end of a bungee cord while the other end is either tied to the wall or
held by a student assistant. This keeps setup time at a minimum.
Experiment 6a: Independence of the
X and Y Motion of a Projectile
There is a common misconception about what will happen when a ball is launched vertically
from a moving vehicle, such as a car. The question “Where will the ball land?” is commonly
answered “Behind the car!” This notion most likely stems from the common experience that a
ball that is thrown up vertically through the sunroof of a car moving forward at moderate speed
will indeed land behind the car. Of course, air resistance is to blame.
Kinesthesia-1 easily remedies this misunderstanding. The PASCO projectile launcher
ME-6830 is mounted at the front of Kinesthesia-1 with a C-clamp. The launcher is oriented
vertically and the launcher is controlled by the student rider.
First, the small ball is launched vertically while Kinesthesia-1
and the rider activating the launcher are at rest (e.g. Fig. 6-1). With
no surprise, the ball returns fairly close to its point of origin. (If the
launcher is perfectly vertical, the ball will hit the muzzle of the
launcher.)
Fig. 6-2: The PASCO Projectile Launcher ME-6830 is mounted on
the Kinesthetics Cart with a C-clamp.
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Fig. 6-1: A ball is launched vertically from a stationary cart
(stationary observer).
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Experiment 6b: Independence of the
X and Y Motion of a Projectile
Now the cart and rider are given a constant velocity in the x-direction. Again the student rider
triggers the projectile launcher. Where will the ball land now? The same spot as for the motionless
cart, in front of the cart, or behind the cart? What is the relationship between the x and y motion?
Please make sure to instruct the rider not to launch the ball prematurely, i.e. while the
cart is given its initial push. The ball should be launched after cart and rider have reached a
constant speed.
Fig. 6-3: A student moving at constant speed launches a small, fluorescent ball vertically. The
student moving with the launcher sees the ball rise and fall vertically. Other students in the class
room describe the motion of the ball as parabolic.
Kinesthesia-1 affords a student the unique opportunity to ride along with the launcher (e.g.
Fig. 6-3). The student riding on the cart sees the ball rise and fall vertically and concludes that the
ball must have the same x-velocity as the cart. The remaining students in the classroom see the
fluorescent ball describe a parabolic trajectory. The relationship between the x and y motion is
parabolic due to the constant gravitational force in the y-direction and the constant velocity in the
x-direction.
It is also possible to mount a video camera on the Kinesthetic Cart and display the purely
vertical motion of the ball on a large video screen (uniformly moving frame). A second video
camera, stationary in the classroom, records the parabolic motion of the ball (laboratory frame).
That the motion is indeed parabolic can be verified using Video Analysis tools.
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Experiment 7: Motion in 2-D
“Uniform Motion vs. Accelerated Motion”
The following experiment is a variation of the one described above. A several foot high tripod
carrying an electromagnet is mounted on Kinesthesia-1, and a target is marked on the surface of
the cart directly below the electromagnet. A small ball bearing (1/4”...1/2”) is released from the
magnet and hits the bull’s eye. Now Kinesthesia-1 moves at constant velocity v. Again the steel
ball hits the bull’s eye. Finally, the steel ball is released while the cart is being accelerated. Why
is it that the steel ball no longer hits the bull’s eye?
Only the upper cart is required for this experiment. This is not a kinesthetic experiment. The
Kinesthetics Cart serves only as a large moving platform.
SUGGESTION: In a larger lecture hall or classroom it might be hard to see exactly where
the ball bearing landed on the target. It might, therefore, be advantageous to replace the target
with a typesetter sorting case or similar screw sorting box, where each compartment contains felt,
cotton balls, or another suitable material, to prevent the ball bearing from bouncing into an adjacent compartment.
➤ NOTE: The setup shown in Fig. 7-1 will also serve as a demonstration when inertial and non-
inertial frames of reference are being discussed
.
Fig. 7-1: A tripod is mounted on Kinesthesia-1 holding an electromagnet. A ball bearing is released
directly above a target by remotely switching off the
electromagnet. This experiment is done for v=0,
v=const., a=const., and a=-const.
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Experiment 8: Newton’s Third Law
The results of physics education research show that the deceivingly simple Third Law is the hardest one for our students to comprehend and accept. Physics education researchers estimate, that by
the time a student manages the action-reaction problems (s)he is 90% converted into a Newtonian
thinker. There is the denial of the reaction: inanimate objects cannot apply forces (e.g., the wall
cannot push against me!), and the familiar student-conception that the stronger, more massive or
more active agent always wins. We can probably agree, that our students grasp the Third Law
fairly rapidly in static situations. However, if, for example, a small vehicle pushes with its bumper
against the rear bumper of a much more massive truck with disengaged engine so that both vehicles move in the forward direction, then the majority of the students will ascribe a larger force to
the passenger car. Their argument: “If the forces between the two bumpers were equally large,
they would cancel and the truck could not start to move in the forward direction”.
Similarly, in the case of the fast moving bus hitting the mosquito, almost all students disallow
the possibility that the mosquito exerts the same force on the windshield of the bus as the windshield exerts on the mosquito.
Kinesthesia-1 again affords a variety of possibilities to illustrate Newton’s Third Law in static
as well as dynamic situations. The “landing gear” of the upper cart and the wheels of the lower
cart are the same kind of roller blade wheels. Thus two carts with identical rolling properties are
available. We equip the students that ride the two carts with spring scales, bathroom scales or
force probes. In many of the possible scenarios we can easily demonstrate the equality of the action and reaction force with a spring scale or bathroom scale. The familiar examples like two students pushing against each other, or one student “simply holding” and the other one pushing, or
the first one pulling and the other one “just holding,” or pushing against an inert object such as a
wall, fall into this category.
However, in dynamic situations such as collisions, where the interaction happens on a millisecond time scale, it is impossible to get a reading from a spring scale or bathroom scale. We offer
here a demonstration that has become feasible in a microcomputer based laboratory (MBL) using
computer interfaced force probes. Priscilla W. Laws has recently introduced a new student activity
that involves the collision of two force probes. Two kinematics carts, both equipped with force
probes facing in the forward direction, approach each other on a track so that the two force probes
collide. The output of both force probes is displayed simultaneously on a computer screen.
This demonstration can easily be modified to incorporate two students into the experiment
using the upper and lower Kinesthetics cart and two heavy duty force probes. This affords both
students a kinesthetic experience combined with the graphical display on a computer monitor in
front of them.
For additional new, impressive illustration of Newton’s Third Law, see Experiments 13
through 16 of this manual.
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Experiment 9: Center of Mass
Conservation of Momentum
➤
NOTE: EXTREME CAUTION IS REQUIRED WHILE PERFORMING THIS EXPERIMENT! This is the only experiment where a
student walks on the plank. In all other experiments students
sit on the cart and hold on to the handles or the cart itself with
at least one hand. To keep the student from injury:
• line both sides of the cart’s path with foam mats
• place spotters along the cart’s path to support the student’s
ascent and descent.
If we align the upper and lower cart and separate them by a distance equal to their length we
can readily clamp 2”x12”x8’ plank to both carts and use it for a number of momentum conservation experiments and center of mass illustrations. A student running from one end of the plank to
the other moves the plank (that is in effect supported by ball bearings) in the opposite direction.
The total momentum of the system is (almost) conserved. The center of mass (almost) stays in its
place.
➤ HINT: If the person walks extremely slowly and very carefully from left to right then the
force exerted on the plank and thus the force exerted on the two carts is too small to overcome
friction (roller blade wheels/ floor). In this case it is possible to walk from left to right without
the plank and carts moving at all. This seems to violate momentum conservation. Of course,
momentum is still conserved, but this time in the larger system containing the floor of the classroom (or the earth). This can be presented to the students in form of a puzzle or extra credit
homework.
Fig. 9-1: As the student moves to the right the plank and the two
Kinesthetics Carts move to the left. This nicely illustrates the conservation of linear momentum in the closed system consisting of the student,
the plank and the two carts.
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Kinesthetic Experience of Non-Linear Forces
Experiment 10: The Simple Harmonic Oscillator
So far we have not yet exposed out students to sinusoidally varying forces. Of course, we could
simply suspend our students from the ceiling using the ever-so-popular bungee cords. However,
for safety reasons we opt for a horizontal simple harmonic motion. Either bungee cords or the
type of springs that we often find on garage doors are suited to convert Kinesthesia-1 into a simple
harmonic oscillator. The oscillation of the student is recorded with a motion detector and displayed
in front of the student while (s)he kinesthetically experiences sinusoidally varying forces.
Figure 10-1: A student riding on the Kinesthetics
Cart undergoes simple harmonic motion.
Experiment 11: The Human Oscilloscope
Finally, we would like to describe a use of the Kinesthetics Cart that has nothing to do with kinesthetic experience but serves to visualize mechanically and macroscopically the basic idea behind
the oscilloscope. A student riding on Kinesthesia-1 rolls at constant velocity v past a blackboard or
a white board. Should neither of those be available, then a roll of old wallpaper works just fine.
Several yards of wallpaper are then unrolled and taped along the wall close to the floor. The student, holding a piece of chalk or suitable marker, moves his/her hand up and down while riding on
the cart alongside the wall, creating a near-sinusoidal graph on the board or back of the wall paper.
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Additional Experiments
Possible With the Collision Attachments SE-8748
The SE-8748 Collision Attachment slides on top of the
Kinesthetics cart with two pegs. It allows the convenient
mounting of 4 empty soda cans that serve as cart
bumpers. Foam inserts in the recesses allow quick replacement of deformed soda cans. Within seconds the
cart will be ready for the next collision.
Rider should push feet firmly against the Collision Attachment during collision experiments.
➤ NOTE: To avoid a great mess, please make sure
that all soda cans are completely empty. Sometimes, a few drops of soda remain in the can. These
can spill out when the cans get crushed or removed
from the holders. It might be worth rinsing out the
amount of cans required for the demonstrations
with tap water.
➤ HINT: Use only soda cans that are not indented
or crinkled. Once the cans are inserted in the Collision Attachment, give each can the same small (few
millimeter) indentation. This ensures that the cans
collapse quite readily and equally. By this method,
the collision experiments work at smaller impact
velocities.
➤ IMPORTANT: Before attempting any collision
experiment it is important to discuss the possible consequences of Newton’s Law on the body. The students need to be aware that their bodies will want to
continue in their state of motion and that they need to
take precautions, such as wearing protective head
gear, maintaining a firm grip on the cart and pushing
firmly against the Collision Attachment.
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Experiment 12: Newton’s Third Law
“A Crushing Experience”
The SE-8748 Collision Attachment impressively brings the excitement of car collisions to our
class room. Aside from the fun of crushing soda cans, students can again get a closer look at
Newton’s Third Law.
Four empty, 12 oz. aluminum soda cans are inserted into the holders of the collision attachment. Instead of simply aiming both carts toward the collision site it is recommended that both
carts are aligned at the collision site so that all four soda cans of one cart touch the cans of the
other cart. The two students participating in the collision position themselves on the carts supporting their feet against the collision attachments and holding on firmly to the carts. Then they
are carefully rolled back to the starting position. Finally, the carts are given their respective impact velocities.
Figure 12-1: Two students are headed for a frontal collision.
Figure 12-2: The soda can bumpers of both carts are equally
deformed thus verifying Newton’s Third Law.
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Experiment 13: Newton’s Third Law Misconception;
“Only the moving object exerts a force”
Physics education researchers have found that some beginning physics students hold on to the belief that
“only the moving object exerts the force.” The object at rest is “being pushed or pulled.”
This conception is readily corrected using a slight modification of Experiment 12. Both cart bumpers
are again equipped with soda cans. However, this time one rider and his/her cart remain at rest. As the
second cart crashes into the stationary cart both sets of soda cans again get equally crushed thus verifying
Newton’s Third Law.
Experiment 14: Newton’s Third Law Misconception;
“The more massive object exerts a larger force”
Here is another example of how Kinesthesia-1 can be used to correct a misconception. Consider
a collision between a heavy truck and a subcompact passenger car. Asked about which of the
two exerts the larger force, students respond confidently, that the truck exerts a much larger force
on the subcompact. This misconception clearly stems from “truck-passenger car collisions” that
students have either witnessed in person or seen on TV. However, the fact that the subcompact
got totaled while the truck escaped with a few dents, is not due to unequal forces, but a consequence of unequal material strength.
We can readily counteract this misconception with Kinesthesia-1 and the collision attachment. We place one light-weight rider on one cart and fit two heavyweight riders on the other
cart thereby approximately tripling the mass of the first cart and rider. (Be sure not to exceed the
maximum load capacity of the Kinesthetics Cart.) Independent of the velocities v
two carts (m1 = m, and m2 ≈3m), the soda cans will be crushed equally, thus again verifying
Newton’s Third Law.
and v2 of the
1
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Experiment 15: Newton’s Third Law Misconception;
“Inanimate objects do not exert forces”
Some students hold on to the notion that inanimate objects do not exert forces. This misconception
is readily counteracted by demonstrating a collision with a wall. One of the collision attachments
is connected to one of the carts and the second collision attachment is mounted to a suitable wall
of the classroom. (To prevent undesirable indentations and scratches to the wall, a several foot
long 2”x12” board can be placed between the wall and the collision attachment.) Again, the students see, experience and comprehend that the force of the cart against the wall is equal and opposite to the force of the wall on the cart, independent of the mass of the cart and rider and independent of the velocity of the cart.
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