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®
Instruction Manual
012-09924A
Spring Cart Launcher
ME-6843
Included Equipment Quantity Replacement Part Number
Spring Cart Launcher 1 ME-6843
Firm Spring (black) 1
ME-6847
1
1
ME-6847 replacement kit includes (2) of each spring and (4) release pins
Medium Spring (blue) 1
Soft Spring (red) 1
Release Pin 2
String 1 m
Required Equipment Part Number
Cart
2
2
This part is included in many of the PASCO dynamics systems. See PASCO catalog or www.pasco.com for details.
1 ME-6951, ME-6950, ME-9430, or ME-9454
Tra ck
2
1 ME-6953 or similar
End Stops
3
3
New-style plastic end stops required. These are included with PASCO dynamics systems starting in 2007.
2 ME-9469 (2-pack)
Recommended Equipment
250 g Compact Cart Mass 2 ME-6755
For sensor-based method:
Motion Sensor
4
4
PASPORT sensors require a PASPORT interface. See PASCO catalog or www.pasco.com for details.
1 PS-2103
Force Sensor
4
1 PS-2104
For traditional method:
Super Pulley with Clamp 1 ME-9448A
Hooked Mass Set 1 SE-8759 or similar
®
Spring Cart Launcher Introduction
2
End stops
Pull
up
Introduction
The Spring Cart Launcher is designed for the study of force and motion, potential
energy, conservation of energy, the work-energy theorem, Hooke’s Law, and spring
constants. Use it to launch any PASCO dynamics cart by compressing and releasing
one of three interchangeable springs. The included release pin, in combination with
two end stops, allows you to use precisely the same spring compression for multiple
launches.
This manual includes instructions for a sensor-based experiment (page 4) using
motion and force sensors, and a traditional experiment (page 6) using hanging masses
and an inclined track.
Set-up and Launch
For this general set-up, you will need the Spring Cart
Launcher with its included springs, launch pin, and string; a
cart; a track, and two adjustable end stops.
1. Fit the Spring Cart Launcher onto
the top of the cart (as illustrated). Tighten the
thumbscrews to secure it.
2. Select one of the included springs. Slide it onto the launcher
shaft with the flared end out. Turn the spring to secure the end in
the spring retention hole as illustrated.
3. Tie the string to the release pin.
4. Install two end stops near one end of a dynamics track between 3
cm and 10 cm apart, measured center-to-center.
5. Place the cart on the track. Push the launcher shaft through the
holes in both end stops.
6. Insert the release pin through
the hole in the end of the
launcher shaft. Allow the
launch pin to rest against the
end stop.
7. To launch the cart, jerk the
launch pin out by pulling
sharply up on the string.
As a simpler, but less repeatable, alternative to the above set-up, use only one end
stop and do not use the launch pin. Pull the shaft through the end stop and release it
from your hand.
Flared
end
Spring
retention
hole
Release pin String
Thumbscrews
®
Model No. ME-6843 Cart Mass
3
Cart Mass
For varying the mass of the cart, the Spring Cart Launcher is designed to hold one or
two Compact Cart Masses (PASCO part ME-6755). The launcher prevents these
masses from shifting or sliding. Place the masses as illustrated.
Theory
The spring constant of a spring is
(eq. 1)
where F
x
is the force applied to the spring and x is the displacement of the end of the
spring from its equilibrium position.
As you push the end of a spring (or anything else) from position x
1
to x2, the work that
you do is equal to the area under the F
x
versus x graph, or
(eq. 2)
The potential energy stored in a spring is
(eq. 3)
The kinetic energy of a cart moving on a track is
(eq. 4)
where m is the mass of the cart, and
V is the magnitude of velocity.
The change in gravitational potential energy of a cart moving up an inclined track is
(eq. 5)
where g = 9.8 m/s
2
, ∆s is the distance traveled along the track (in the uphill direction),
and θ is the track’s angle of incline.
Masses
k
F
x
x
------=
Spring constant
WFxxd
x
1
x
2
∫
=
Work done on a spring
U
spring
1
2
---
kx
2
=
Potential energy stored in
a spring
K
1
2
---
mV
2
=
Kinetic energy
∆U
gravity
mg∆s θsin=
Potential energy of a cart
on an inclined track
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