Work & Energy, Circular Motion
Purpose:
To apply the WorkEnergy Theorem to a reallife problem.
To investigate the
forces and accelerations associate with circular motion.
Apparatus:
Hot Wheels car, Hot Wheels track, Hot Wheels car launcher, masking tape,
timer, meter stick, Flying Cow hanging from string, spring scale (blue).
Introduction
The first activity of this lab is a complex problem that is to broken up into two main parts
 Work & Energy and Circular motion.
You will determine the energy stored in a Hot
Wheels launcher and use that value to predict the
minimum
launcher setting that will
enable the Hot Wheels to execute the looptheloop successfully
on the first try
.
The second activity involves investigating the acceleration and forces on a Flying Cow
going around in a circle.
Theory
The WorkEnergy Theorem
States that
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(in words)
The net
work
done on an object equals its change in kinetic energy.
(in Mathematics)
W
=
KE
f
−
KE
i
(1)
Recall that the kinetic energy of an object is
KE
=
1
2
mv
2
The
work done on an object
is given by
W
=
Fcos
s
where
s is the distance over which the force acts and
the angle between the force and
the displacement.
For a single mass dropping to the floor from height h, the only force
doing work (causing motion) is the gravitational force on the small mass, mg, which acts
over the distance h, the height from which it drops to the floor.
We can now expand on equation (1):
mgh
=
1
2
mv
f
2
−
1
2
mv
i
2
(2)
The quantity
mgh
is the potential energy the mass acquires as it is moved from the floor
(zero potential) to its starting point (mgh potential).
(Incidentally, we could also have
assigned zero as the potential energy before the fall and mgh the potential on the floor)
You can therefore read equation (2) as “the potential energy of a falling small mass is
converted to its kinetic energy”.
Note that you can also read the equation
backwards
, as
in “a small mass thrown in the air has its kinetic energy converted to potential energy”.
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 Fall '08
 RICHARDSON, B
 Physics, Acceleration, Circular Motion, Energy, Force, Potential Energy, Work, WorkEnergy Theorem, hot wheels car

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