Mass driver: One of these balls is not like the other

• D+35+16

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.