SCI 8
ENERGY IN A BOUNCING BALL
What happens to the energy of a ball as it falls from a height and bounces on the ground?
We will be analyzing the energy changes in several different balls as they are dropped.
The report for this lab consists of your answers to all of the questions that are labeled
with a Q.
Q1. As a preparation for this lab, use your text to define the following terms and give
an example of each: energy, kinetic energy, potential energy, the law of conservation of
energy.
Answer these questions by an experiment:
Does a ball lose energy as it bounces ?
Does the ball lose the same percentage of its energy with every bounce?
Do different kinds of balls lose the same percentage of energy when they bounce?
PROCEDURE
1. Have your partner hold a meter stick vertically, with the zero end on the floor, and in
such a way that it can be read easily by you. Your partner should hold the bottom of
the golf ball at the 30 cm mark and release it. You must quickly note the height to
which the bottom of the ball returns on its first bounce. Record the data in Table 1.
2. Repeat step 1 three more times and record the results.
3. Repeat steps 1 and 2, but this time drop the ball from a height of 60 cm.
4. Do this for 90,120 and 150 cm. Record all data in Table 1.
5. Calculate the average bounce for each height and record in Table 1.
6. Repeat the whole procedure with a tennis ball and record all data and calculations in
Table 2.
7. To find the percentage of energy lost after the bounce you can assume that the energy
is directly proportional to the height and that the percentage change in height will also
express the percentage change in kinetic energy of the ball. In other words, the height
is a good measure of the potential energy of the ball.
% loss of energy = % loss of height = original height - bounce height X 100
original height
Q2. Use the above formula to calculate the % energy lost at each initial height (use the
average bounce height) and record in the appropriate table.
Q3. Which loses energy faster, the golf ball or the tennis ball? Is this what you expected?
Explain.
Q4. Make a line graph of Initial Height (independent variable) Vs Bounce Height for both
balls on the same axis. Also on this same set of axes, draw a line which would represent a
hypothetical “perfect” ball which did not lose any energy as it bounced.
Q5. Is it reasonable to expect straight lines for this graph? Explain your answer.
Q6. Use the graph to predict how many bounces would be necessary before each ball
stopped bouncing.
Q7. At which point in the experiment did the ball have the most potential energy?
Q8. At which point in the experiment did the ball have the most kinetic energy?
Q9. Describe how the potential and kinetic energy values for a ball that is allowed to
bounce continually are changing.
Q10. The law of conservation of energy states that energy cannot be lost from a system. If
this is true, then explain what happened the energy that was apparently lost as the balls
bounced?
Q11. Hand in the completed Tables I and 2 with your report.
Table 1: bounce heights and energy lost for a golf ball
Initial Height
(cm)
Bounce
height
trial 1
Bounce
height
trial 2
Bounce
height
trial 3
Bounce
height
trial 4
Bounce
height
average
% energy lost
30
60
90
120
150
Table 2: bounce height and energy lost for a tennis ball
Initial Height
(cm)
30
60
90
120
Bounce
height
trial 1
Bounce
height
trial 2
Bounce
height
trial 3
Bounce
height
trial 4
Bounce
height
average
% energy lost
150