5K40.49a - Mystery Top

Code Number:
5K40.49a
Demo Title:
Mystery Top
Condition:
Excellent
Principle:
Motors, Elec. & Mag.
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 continuous running.  The top runs at approx. 2500 rpm and 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.

Disclaimer: These demonstrations are provided only for illustrative use by persons affiliated with The University of Iowa and only under the direction of a trained instructor or physicist.  The University of Iowa is not responsible for demonstrations performed by those using their own equipment or who choose to use this reference material for their own purpose.  The demonstrations included here are within the public domain and can be found in materials contained in libraries, bookstores, and through electronic sources.  Performing all or any portion of any of these demonstrations, with or without revisions not depicted here entails inherent risks.  These risks include, without limitation, bodily injury (and possibly death), including risks to health that may be temporary or permanent and that may exacerbate a pre-existing medical condition; and property loss or damage.  Anyone performing any part of these demonstrations, even with revisions, knowingly and voluntarily assumes all risks associated with them.