Bouncing Ball Lab
We have talked about the First Law of Thermodynamics which relates the total energy of a system to
the work done on its surroundings and the heat exchange with those surroundings. In this lab, we will
explore how this fundamental prinple will help to understand an apparent loss of energy in a collision.
This lab requires a few materials.
• A few spherical sports balls (baseball, basketball, tennis ball and/or raquetball)
• A meterstick or paper marked with centimeters
• A triple beam balance
Once these materials have been collected you may begin the lab.
Lost Energy?
Introduction
In this first section of the lab we will determine how much energy is “lost” in a collision. We will discuss
where this energy goes and how we measure it.
Procedure
Follow these instructions carefully. Ask questions before acting. Make sure that one partner is ready to
catch the ball after the collision!
• Obtain a sports ball and weigh it on the triple beam balance.
• Using the paper to measure height, one partner should drop the ball from 1m, measured from the
bottom.
• After the collision, the other partner should measure the bounce height using the bottom of the ball
as your reference.
• Make sure that your ball bounces vertically. If it bounces at an angle, redo the measurement. This
particullary important for ball with seams or stiching (baseball and tennis ball).
• Perform this experiment 10 times, recording the bounce height each time.
• Compute the average height and standard devation of your measurements.
• After all groups have performed measurements, record all groups measurements and the ball that
each group used.
Discussion
Your instructor will ask you to compute the following quantities. Use the appendix, if you’d like.
• Initial and Final Gravitational Potential Energy (before and after collision)
• Initial and Final Kinetic Energy (before and after collision)
• Initial and Fianl velocity (before and after collision)
Think about your measurements while answering these questions.
• Which ball’s bounce height was closest to the original height?
• How can we compute the “lost” energy?
• Energy cannot be created or destroyed, where did this energy go?
• How precise are your measurements?
Baseball Companies
Introdution
Sports ball manufacturer use one number to determine whether a ball truly passes inspection. This
number is the “coefficient of restitution”, CR . This number measures the “springy-ness” of a material.
For sports ball manufacturers and major league sports organizations, this number is stricty monitored
and enforced. We can measure this quantity to determine whether our sports balls pass inspection.
This is a simple computation, your instructor will discuss how it is used by the industry.
Discussion
Compute the coeffient of restitution for your measurements. See the appendix for the formula. Notice a
coefficient of 1 implies an perfectly eleastic collision.
Record other groups coefficients.
Acceptable values are:
Sports Ball
Baseball
Basketball
Tennis Ball
Hand Ball
Ping Pong Ball
Super Ball
CR
0.51
0.60
0.68
0.72
0.57
0.65
Appendix
The Energy Principle
∆E = W + Q
Kinetic Energy
1
K = mv 2
2
Gravitational Potential Energy
U = mgh
Coeffcient of Restitution
s
hbounce
CR =
hdrop
Average of Measurements
n
1X
x=
xi
n
i=1
Standard Deviation
v
!
u
n
u1 X
2
2
t
σ=
xi − n x
n
i=1
Percent Error
% error =
|observed value − true value|
true value