Physical Science
Unit 8 - Lab #3 Energy of Falling Motion
Name:__________________________
Investigating Energy and Falling Motion
Background Information
When an object such as a ball falls, it accelerates and acquires kinetic energy, or energy of
motion. If it does not reach terminal velocity, it acquires its maximum velocity and
therefore its maximum kinetic energy just as it hits the ground. At that point, its motion
is stopped and it is compressed. The kinetic energy is momentarily converted to potential
energy, or stored energy. This potential energy is then converted back to kinetic energy
as the ball bounces back. No ball will return to the exact height from which it was
dropped because some of the kinetic energy is converted to other forms of energy, such as
heat, when the ball strikes the ground. According to an important principle known as the
law of conservation of energy, however, the total amount of energy does not change
Problem
How can the motion of a bouncing ball be described and accounted for in terms of energy?
Materials
Meter stick
Tennis ball
Ping-Pong ball
Golf ball
Marble
ball
ground
50
40
30
20
10
Figure 1
Procedure
 Mass each of the four objects being tested in this activity and record the mass on the data
table.
 Have one member of your group hold the meterstick upright with the zero mark on the
floor, as shown in Figure 1.
 Have a second member of your group drop the tennis ball from the top of the
meterstick (100cm mark) in such a way that it does not touch the meterstick on
the way down.
 Have a third member of your group note the height of the first bounce. The
bounce height should be called out to the fourth member of the group, who should
record it in the Data Table. Let the ball continue to bounce and continue
observing it for as long as you can. (It may take several trials because the ball
may tend to bounce away from the meterstick.)
 Repeat steps 1, 2, and 3 for all four of the objects.
 Make a separate graph for each of the objects tested. Plot the height of each
bounce on one axis, and the bounce number (i.e. bounce #1, bounce #2 , etc.) on
the other axis. Which is the independent and which is dependent variable?
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Physical Science
Unit 8 - Lab #3 Energy of Falling Motion
Name:__________________________
Data Table
Type of Ball
Mass of
object
First
Bounce
Second
Bounce
Third
Bounce
Fourth
Bounce
Fifth
Bounce
Tennis Ball
Ping-Pong Ball
Golf Ball
Marble
2
Physical Science
Unit 8 - Lab #3 Energy of Falling Motion
Name:__________________________
Analysis:
1.) Which ball retained the greatest percentage of its mechanical energy (had the
most elastic collision) on the first bounce? Be sure to show your calculations of
PE at 100cm and height of 1st bounce. Then calculate the percentage retained.
2.) Explain the shape of each line on the graphs in terms of energy. Why were the
shapes similar? Were there any graphs that differed greatly from the others?
Explain why the differences might have occurred.
3.) Why can’t a ball bounce higher than the height from which it is dropped?
Explain your answer in terms of energy.
4.) Suppose you had carried out this investigation using a carpeted floor. How
would your results have differed? Be sure to explain your answer in terms of
energy conservation.
5.) Is there a relationship between the mass of an object and its ability to retain
mechanical energy? Explain your answer using your data and graphs.
The percentages from question #1 could be helpful.
6.) Draw 4 bounces of the superball and use arrow to indicate the transfer of
KE to PE to KE, etc.
7.) Explain why all the balls ended with no energy. Where did it go and how do
you know this?
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Physical Science
Unit 8 - Lab #3 Energy of Falling Motion
Name:__________________________
8.) Calculate the PE of each ball at the 100.00cm mark and the KE of each ball
at the 25.00cm mark as it falls. Remember that total ME in a system is equal to PE
+ KE. Assume no energy lost due to air resistance. You must show all work for
full credit
Ball
Tennis Ball
Ping-Pong Ball
Golf Ball
Marble
PE (100.00cm)
KE(25.00cm)
Conclusions:
What did you do? What did you find? What generalizations can you make?
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