One of These Balls is Not Like the Other

Three, seemingly identical, steel balls are set up at the end of an aluminum track. When one more is rolled down the track towards the series it is attracted strongly to the set of three and the front ball in the series is launched off at a high rate of speed. The students can then be challenged to describe what happened and why. The explanation is that one of the balls is a magnet. This demo is functionally identical to D+35+15, just on a different track and with a spherical magnet rather than an obvious cylindrical one.
UCB Index: 
Demo Diagram: 



The track (made out of Al) and the spherical magnet are stored in 33+4 in Pimentel. The steel balls used are the same as in A+35+5.

Tis can be presented in several different ways. The demonstration can be done and then you can invite the participant to explain it or, if more time is available, you can hand the participant the materials to make the demo work and challenge them to figure out how to launch the ball. As always when you present a demo make sure you ask the participants questions before you demonstrate and after. Think about the concepts involved beforehand; having a friend ask you questions about it can be very revealing as to if you understand it well or not. Whenever you ask a question count to five (or at least three) in your head waiting for an answer before you stay anything else.