Magnetic Friction

[Guest Lester Ani Ben]

Suppose you have a spinning object rotating in a cylinder propelled from the bottom and sides by magnets and have no friction. If you spun the object, and then let it spin forever without any air, static, rolling, or sliding friction, would the object spin forever, or would the magnets have an electromagnetic friction that would cease the object to move eventually?

 

Note: the object spinning would be given an initial force but from then on no other forces are applied except from the magenets.

 

Thanks.

[mustang292]

I can only tell you that it must be perfectly alligned. I tried an experiment for fun where I took a circle of magnets on an axle and held a single one up to it with reverse polarity and spun the axle to see if it would keep on spinning. It always ended up stopping because I could never get the circle of magnets perfectly alligned.

 

I did it to try and prove to a friend that on a larger scale it could be used in cars if your gas peddle was the single magnet and the axle was reversed polarity. Well a fun thought, but not enough $$ to actually get the materials I would need to build a large scale.

[swansont]

The surroundings, if they conduct, would likely get eddy currents from the changing magnetic field. From Lenz's law, those would create fields that oppose the change and that draws energy from the spinning object.

 

There is a neat demonstration of dropping a magnet down a conducting tube - the fall is much slower than in free space because of this effect.