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Work Done By Springs
On An Air Glider
John Domanick
10/12/10
Partners: Jordan Pardo, Matt Weiner
Teaching Fellow: Tim Harden
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View Full Document Abstract:
In this experiment we investigated the force of two springs on a glider on an
air track.
Specifically we investigated how measured forces at specific interval of
spring stretch compare to those theoretically predicted for the same stretch
distances. We also then compared the work done by the springs on the glider to the
change in kinetic energy of the glider, to verify the work‐energy theorem. We know
that springs exert position dependent forces on the body on which they act, and
there should be no difference in these forces, whether measured static, as an
equilibrium measurement, or dynamically, by measuring acceleration of the body
due to the force. We also know that the work a force does is equal to the change in
kinetic energy of the object the force acts on, and again there should be no
difference in the work if we measure statically as an integral of a function of forces,
or dynamically as the kinetic energy of the object.
We found that in each part of our experiment the static and dynamic
measurements of both force and work are not in agreement. The forces we
measured only agreed 4 out of 11 trials, and only just. The work we measured,
statically was 0.040J, and kinetically was 0.046018+/‐1.68145x10
‐9
J.
Theory:
The force that a spring exerts on a body is a position dependent force, that is
to say, that the force varies with the distance that the spring is either stretched or
compressed. An ideal spring follows Hooke’s Law, and the force is equal to:
F
s
=
−
kx
(1)
where k is the spring constant, essentially the stiffness of the spring, and x is
the stretch/compression distance from its equilibrium point.
To predict the force of the spring at various points of stretch, we attached
multiple known masses to the springs, over a pulley. Here we knew that once the
spring reached its new equilibrium point, that the spring’s force would be equal to
the tension in the string connecting the weight and springs, and that the tension was
equal to the force of gravity on the weight.
F
g
=
mg
=
F
T
=
F
s
(2)
To measure the experimental force of the springs on the glider, we had to
measure the acceleration of the glider as it passed through each of the equilibrium
points, previously determined with known masses. Using a photogate system we
were able to measure the acceleration of the glider along its motion. We could then
calculate the force of the springs on the glider by:
F
net
=
ma
=
F
s
(3)
where a is the acceleration of the glider at the equilibrium point, and m is the
mass of the glider.
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This note was uploaded on 10/06/2011 for the course PHYS 19 taught by Professor Blocker during the Fall '10 term at Brandeis.
 Fall '10
 blocker
 Force, Work

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