Apparatus Competition

2006 AAPT Summer Meeting

Syracuse, NY


Follow The Bouncing Ball


Clifford Bettis

116 Brace Lab

Dept. of Physics and Astronomy

University of Nebraska-Lincoln

Lincoln, NE  68588-0111



cbettis ‘at’ uniserve ‘dot’ uni ‘dot’ edu



This apparatus is an intriguing hallway demonstration. It obviously shows elastic collisions but it also raises the question of what the secret is to the stability of the bouncing ball. Most often the public guesses that it has something to do with magnetism.

Construction of Apparatus: 

The apparatus is constructed out of  a 6” x 1” disk of A2 tool steel that is machined with a computer controlled milling machine so that one surface has a radius of curvature of 1 m. Threaded holes for leveling screws are added and then the disk is surface hardened by heating and quenching. The ball is a ¼”  hardened steel ball bearing.

Use of Apparatus: 

I use it as a hallway exhibit. Children and their parents are particularly intrigued by it.