By turning on the flashlight and rotating the wheel, it will simulate epicyclic motion.

A very simple demo useful for demonstrating epicyclic motion.

1. The bicycle wheel has a flashlight mounted to the SIDE of the wheel (that is, the flashlight's beam will point along the angular momentum axis of the wheel). The light should face towards the audience. 2. With the instructor stationary, spin the wheel and hold the axis of the wheel so that the class sees the flashlight moving in a circle (pointing out into the audience) 3. Walk across the front of the lecture hall (maintaining the flashlight always pointing 'out into the audience') to illustrate that sometimes the light appears to be moving to the right, and sometimes to the left (retrograde). 4. The fraction of time retrograde depends on the wheel's rotation rate relative to the walking rate.

Edited: Jan 18th, 2016