Energy of a Tossed Ball Lab Report

Lab 7 “Energy of a Tossed Ball.”Motion Detector
In this experiment, we will study energy changes using a Motion Detector.
OBJECTIVES:
• Measure the change in the kinetic and potential energies as a ball moves in free fall.
• See how the total energy of the ball changes during free fall.
MATERIALS:
Computer
Lab Pro
Logger Pro
Vernier Motion Detector
Basketball;
PRELIMINARY QUESTIONS:
For each question, consider the free-fall portion of the motion of a ball tossed straight upward, starting just as
the ball is released to just before it is caught. Assume that there is very little air resistance.
1. What form or forms of energy does the ball have while momentarily at rest at the top of the path?
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2. What form or forms of energy does the ball have while in motion near the bottom of the path?
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3. Sketch a graph of velocity vs. time for the ball, kinetic energy vs. time for the ball, and potential energy
vs. time for the ball.
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PROCEDURE:
1. Measure and record the mass of the ball you plan to use in this experiment.
2. Connect the Motion Detector to the DIG/SONIC 1 channel of the interface. Place the Motion Detector on
the floor and protect it by placing a wire basket over it.
3. Hold the ball directly above the Motion Detector. Have your partner click
to begin data
collection. Toss the ball straight upward above the Motion Detector and let it fall back toward the Motion
Detector catch the ball before it hits the detector.
Note: Use two hands, be sure to pull your hands away from the ball after it starts moving so they are not
picked up by the Motion Detector. Throw the ball so it moves vertically above the detector. Verify that
the position vs. time graph corresponding to the free-fall motion is parabolic in shape, without spikes or
flat regions, before you continue. This step may require some practice. If necessary, repeat the toss, until
you get a good graph. When you have good data on the screen, proceed to the Analysis section.
4. Click on the Examine button, , and move the mouse across the position or velocity graphs of the
motion of the ball to answer these questions.
a. Identify the portion of each graph where the ball had just left your hands and was in free fall.
Determine the height and velocity of the ball at this time. Enter your values in your data table. (after
release)
b. Identify the point on each graph where the ball was at the top of its path. Determine the time, height,
and velocity of the ball at this point. Enter your values in your data table. (top path)
c. Find a time where the ball was moving downward, but a short time before it was caught. Measure and
record the height and velocity of the ball at that time. (before catch)
d. Collect two more times on the way up and on the way down for a total of seven data points.
e. For each of the seven points in your data table, calculate the Gravitational Potential Energy (GPE),
Kinetic Energy (KE), and Total Energy (TE). Use the position of the Motion Detector as the zero of
your gravitational potential energy.
DATA TABLE:
Mass of the ball
(kg)
0.5
When
Time (s)
Position (m)
Velocity (m/s)
GPE (J)
KE (J)
TE (J)
After release
3.95
0.981
1.251
4.90
0.391
5.29
On the way up
4.00
1.035
0.770
5.18
0.148
5.33
Before the Top
4.05
1.059
0.284
5.30
0.020
5.32
Top of path
4.10
1.062
-0.173
5.31
0.074
5.38
After the Top
4.15
1.043
-0.641
5.22
0.103
5.32
going down
4.20
0.998
-1.105
4.99
0.305
5.30
Before catch
4.25
0.932
1.572
4.66
0.618
5.28
ANALYSIS:
1. Use Logger Pro and graph the energies as a function of time. Please show all energies on the same
graph and their corresponding mathematical equations ( Kinetic Energy and Gravitational Potential
Energy are quadratics, Total Energy is a straight line)
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2. Inspect your kinetic energy vs. time graph for the toss of the ball. Explain its shape.
3. Inspect your gravitational potential energy vs. time graph for the free-fall flight of the ball. Explain its
shape.
4. Inspect your Total energy vs. time graph for the free-fall flight of the ball. Explain its shape.
5. What do you conclude from this graph about the total energy of the ball as it moved up and down in
free fall? Does the total energy remain constant? Should the total energy remain constant? Why? If it
does not, what sources of extra energy are there or where could the missing energy have gone?
6. Explain the role play by the work done by the gravitational force in the energy changes.
7. What is a conservative force? Examples
8. What is a non-conservative force? Examples?
9. What would change in this experiment if you used a very light ball, like a beach ball?
10. Use Logger Pro bar graph option to create an Energy graph.
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11. What would happen to your experimental results if you entered the wrong mass for the ball in this
experiment?
CONCLUSION:
I.
Definitions:
•
Work
•
Kinetic Energy
•
Gravitational Potential Energy
•
Conservation of Energy
•
Power
II.
Meaning of the slope and the y-intercept for the Total Energy vs. time graph.
III.
Equations: How do you calculate or state mathematically the above definitions.
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