Noise maker with battery attached to string
Take the battery and connect the wires to the battery. When the wires are connected a high pitch sound can be heard. Take the string and begin to spin the battery and noise maker around in a circle above your head.
Make sure that you have plenty of room to spin the noise maker without hitting any objects in the room. Also experiment with the speed of the spinning so that the students can hear subtle changes. Also make sure to test the noise maker to make sure that the battery is in working order before you perform this demonstration in class.
fl = frequency of listener, fs = frequency of source, vl = velocity of listener, and vs = velocity of source
The velocity of the listener is positive when the listener is headed towards the source and negative when the listener is headed away. The velocity of the source is positive when the source is headed for the listener and negative when the source is headed away from the listener. when the source or listener are stationary their velocity would be zero.