Mathematics/Physics

 

Bouncing Balls

 

Porter Johnson

Illinois Institute of Technology

BCPS Department

CHICAGO IL 60616-3793

(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:

 

  1. A supply of several super balls of various shapes and sizes. [They are conveniently available at a local science supply house, or simply order them from American Science and Surplus at http://www.sciplus.com.]
  2. Several one-meter rulers, and at least one two-meter stick.
  3. Several other types of balls; i.e. tennis balls, ping-pong balls, steel balls, wooden balls, rubber balls, and marbles.
  4. A Happy/Unhappy Ball Set from a local science supply house, or from American Science and Surplus at http://www.sciplus.com.

 

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:

http://www.superballs.com/.

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.