How Everything Works
How Everything Works How Everything Works

Question 648

I have heard of a magnetic top that will spin on top of another magnetic field because of the gyroscopic effect. If that is put into a vacuum chamber, would it spin perpetually? — JH, Visalia, CA
Probably not. The magnetic top that you mention is a wonderful invention, sold under the name "Levitron". It uses gyroscopic precession to stabilize what is normally an unstable arrangement: two oppositely aligned magnets, one supporting the other. In air, you can get the Levitron top to stay aloft for a couple of minutes before its spin rate declines to the point where it stops being stable. In a vacuum, I'd expect it to last much longer but not forever. Thermodynamics overwhelms just about everything sooner or later and the Levitron won't be an exception. Even if you get rid of air resistance, the spinning top's strong magnetic field will interact with its environment and will allow the top to exchange energy with that environment. While there is always the possibility that these exchanges will make the top spin faster, such favorable exchanges are relatively unlikely. Instead, the energy exchanges are much more likely to extract energy from the top and slow it down. For example, any conducting surfaces near the Levitron top will exert a magnetic drag force on the top and will convert its energy into thermal energy in those conducting surfaces. Forever is a long time and the top will certainly slow to a stop eventually. Still, it might be interesting to see how long it can stay spinning. I'll bet 10 minutes is the realistic maximum. If I have a chance to test it out, I'll let you know what happens.

Copyright 1997-2017 © Louis A. Bloomfield, All Rights Reserved
Privacy Policy