Code Number: 5K40.49a
Demo Title: Mystery Top
Condition: Excellent
Principle: Motors, Electricity and Magnetism
Area of Study: Perpetual Motion
Equipment:
Mystery Top Demo, Fresh 9-Volt Battery.
Procedure:
See also 5K40.49a in Electricity and Magnetism.
The top demo is really a specially designed brushless DC electric motor. The small top corresponds to the rotor and flywheel of a motor. It actually has a small bar magnet in it. In the base are a battery, coil, steel core, and transistor. These create the magnetic field that power the small top. As the small top moves around on the surface of the base the motor is turned on and off by the top leaving and entering the small magnetic field which is concentrated at the center of the base. The transistor is nothing more than a sensing switch. The battery should last for 5 to 7 days of continuous running. The top runs at approx. 2500 rpm at full battery strength.
References:
- Arthur Schmidt, Peter Insley, "Perpetual (?) Spinning", TPT, Vol. 22, # 9, Dec. 1984, p. 594.
- H. Richard Crane, "A Spinning Top, Lenz's Law and Electric Watches", TPT, Vol. 22, # 2, Feb. 1984, p. 113.
- C. L. Stong, "An Electrometer, a Temperature Control Apparatus, and a Simple Electric Motor", The Amateur Scientist, October, 1965.
- Jodi and Roy McCullough, "Electromagnetism with a Perpetual Motion Top", The Role of Toys in Teaching Physics, p. 4.200.