Additional Info

• ID Code: C7-18
• Purpose: Shows velocity multiplication in colliding balls
• Description:
  

  This device has four balls of graduated masses on a central shaft. The smallest has a slightly larger opening so that it can come off the shaft, while the others are trapped in place. If the whole assembly is dropped from 50cm or so about the table, the smallest ball on the end will fly off with considerable velocity, potentially rising to significantly greater than the initial height.

  Please be careful not to lose the small ball, and do not launch it into the audience or at anything else breakable.

  Engagement Suggestion

  • When presenting this device, describe it clearly, then encourage students to predict what will happen when you drop it.
  • Afterwards, have them discuss the results.
  

  Background

  The total energy of the system, of course, cannot increase beyond what it gains from the potential energy of the height from which it is dropped. But the elastic collisions of each ball with a successively smaller and less massive one transfer significant kinetic energy. With the smaller mass of the final ball, it can have a higher velocity than the collection as a whole did.

• Availability: Available
• References: Mancuso&Long, "The astro-blaster," TPT33 (1995)
• Loc codes: C7
• Videos-1: Demonstration video on YouTube