Mathematics/Physics
Bouncing
Balls
|
Porter
Johnson |
Illinois
Institute of Technology |
|
406
N Elmwood Avenue |
BCPS
Department |
|
OAK
PARK IL 60302-2226 |
CHICAGO
IL 60616-3793 |
|
(708)
383-2846 |
(312)
567-5745 |
Objectives:
A
ball bouncing on a hard surface is used to study the action of gravity on a
simple system. We will let a single
ball bounce several times, as well as having several different types of balls
to bounce off a hard surface.
Materials:
Strategy:
First, take a super ball and drop it from a height of one meter directly over one of the squares in a floor tile, if there is a tiled floor in your classroom. Count the number of times the ball bounces before leaving the square in question, and record the number. Do this several times. Then, drop a super ball of a different size over the square, and record the numbers. Repeat the experiment while dropping from heights of ˝ meter and 2 meters, respectively. You should observe that the ball only bounces a few times within the square, no matter how carefully you may drop it. When you drop it from a greater height, it makes fewer bounces inside the square, and more when you drop it from lower height.
Next, divide the class into teams, and have each
team to release a super ball at rest from a height h0 of one meter,
and measure the height h1 to which the ball rises on first
bounce. Each team should record its
bounce height in a table on the blackboard.
Next, measure the height h2 for the second bounce. Note that
h2 / h1= h1 / h0.
Bounce the ball from a height of 2 meters, and show
that this relation is still valid.
Try bouncing the super ball off a steel plate [if
available], and observe that it bounces much higher.
Show that the super ball bounces much better than
most other balls, such as ping-pong balls, tennis balls, or ordinary rubber
balls. Also, drop the “happy ball, sad
ball” set, to show that two balls may appear to be very similar, and yet bounce
quite differently.
Finally, drop a little super ball that lies on top
of a big super ball. [You may wish to
cut out a little trough in the big super ball with a sharp knife.] After the bounce, the big super ball hardly
bounces at all, whereas the little super bounces to far above the height of
release. Why? See the website given below.
Performance
Assessment:
Give each student a super
ball, with the objective of having the ball to bounce back and forth, while
remaining close to the initial location. It takes a certain amount of practice
for you or the student to learn how to do this, and to accomplish it you must
give the ball both a spin and an initial horizontal motion. The initial velocity and angular velocity
should be opposite in direction, and comparable, for this to work. Each student is given a passing grade when
he/she learns to accomplish this task.
Conclusions:
The bouncing ball is used as a tool to illustrate
motion, collisions, and behavior of a body in motion.
References:
Bouncing Ball JAVA Applet:
http://www.phy.ntnu.edu.tw/java/bouncingBall/bouncingBall.html
You
may vary the elasticity of this ball, as it bounces freely across the floor.
Super
ball Home Page:
Learn
about all aspects of super balls.
Super
ball Rocket Launcher:
http://www.physics.gla.ac.uk/gusto/pubsci/exhibits/d12/index.htm
Study
of bouncing the big ball with the little ball on top.
Indiana
University Demonstrations on super balls [and other things] at the site:
http://www.physics.indiana.edu/~demos/mechdemo.htm.
Several
super ball demonstrations are included in this package.