Download Energy Tracks Lab Name Objective: Examine the concept of the

Energy Tracks Lab
Name ________________________
Objective: Examine the concept of the conservation of energy.
Background: The law of the conservation of energy states that energy cannot be created or destroyed – only converted
between one form and another. In order to raise the ball to the release point at the top of the tacks, one must exert
energy. Work, another term for energy, is being performed on the ball in order to raise it. Work is defined as a force
used through a distance. It requires work to move any object. The energy used to raise the ball to a position higher than
the reference point is “stored” on the ball. The ball has gravitational potential energy. This potential energy can be used
later to do work. The potential energy of the ball is related to its height and weight. The gravitational potential energy is:
GPE = mgh, where m is the mass, g is the magnitude of the acceleration due to gravity and h is the height
As the ball begins to move down the track the gravitational potential energy is converted into kinetic energy. For a
rolling ball, the ball travels in a straight path down the track and it rotates. The ball has both translational kinetic energy
and rotational kinetic energy. Translational kinetic energy is related to the mass and the linear speed of the ball.
Rotational kinetic energy is related to the moment of inertia of the ball (resistance of an object to change its rotational
motion) and the rotational speed of the ball.
In this lab we will assume that the ball will roll down the track without slipping. The energy will not be converted into
thermal energy. All the gravitational potential energy the ball has at the top of the track will be converted into
translational kinetic energy and rotational energy at the bottom of the track. The mechanical energy at the top of the
track equals the mechanical energy at the bottom of the track.
If the object slides then the kinetic energy is only translational kinetic energy. The mean
(GPE)top = (KE)translational
mgh = ½ mv2
The linear speed of the ball would be
v  2 gh
If the object is rolling then there is also rotational kinetic energy and
mgh = ½ mv2 + (KE)rotational
The picture below shows the four tracks labeled A – D. Make sure you can identify the tracks for future questions.
Procedure:
1. Ask your teacher for the steel ball. Make sure your tracks are set up so that when you place the steel ball on
each of the tracks, the steel ball moves without a push.
2. Calculate the gravitational potential energy of the ball at the top of each track. The mass of the ball is 0.00282
kg. Measure the height of the track in meters.
3. If friction is ignored, what is the kinetic energy at the bottom of each track? Explain your answer.
4. The speed of a rolling ball has two components: the linear speed due to the translational kinetic energy and the
rotational speed due to the rotational kinetic energy. The linear speed calculation for the ball is more
complicated. Calculate the linear speed of the rolling ball at the bottom of the track using the equation below.
v  10 / 7gh
5. Make sure that your photogates are set up at the bottom of the tracks so that the ball will roll down track B
without bumping into the photogates.
6. Open Logger Pro 3.8 on your desktop. Open Physics with Vernier and then Exp 08 Projectile Motion.
7. Measure the distance between the photogates from one leading edge to the other and enter that value in
meters into the gate spacing box in the program.
8. Click COLLECT and roll the ball down track B 5 times. The program will calculate the speed of the ball. Enter
these values into the table below and calculate the average speed.
Trail Number
Speed (m/s)
Average speed of the
ball at the bottom of
the track =
___________ m/s
1
2
3
4
5
9. Compare the calculated speed and the measured speed. Explain your answer.
10. How would the speed of the ball change if the ball was more massive? Explain.
11. How would the kinetic energy of a dropped ball compare to the kinetic energy of a ball rolling down a track if
both balls started at the same height? Explain.
12. How would the linear speed of a dropped ball compare to the linear speed of a ball rolling down a track if both
balls started at the same height? Explain.
13. What is the energy trail for the ball rolling down the tracks?
____________________  ___________________
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