A fixed magnetic field will induce an electrical current in a conductive object moving through the field. The strength of the eddy currents will depend on the shape and composition of the conductor and also how fast it is moving. The electrical current produces ohmic heating in the conductor, and some of the kinetic energy of the moving conductor will be turned to heat. This is how induction brakes work.

I wonder if this principle applies to fast moving conductors like asteroids or satellites that encounter planetary magnetic fields. Are planetary magnetic fields strong enough to act as induction brakes on moving conductors? A satellite experiencing induction braking would fall to a lower and lower orbit and eventually out of orbit. Passing asteroids might have their course deviated more than would be expected just from gravity.

My search turned up only this abstract, which attempted to explain why meteorites are hot via this principle.


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  • $\begingroup$ Low Earth orbit speed is 7.8 km/sec. I have not heard of this type of heating or effects on orbits in the Space Age. $\endgroup$ Feb 6, 2019 at 3:22
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    $\begingroup$ Sort of related: en.wikipedia.org/wiki/Electrodynamic_tether $\endgroup$
    – PM 2Ring
    Feb 6, 2019 at 5:12
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    $\begingroup$ @PM2Ring You could totally make an answer out of that, it's very much related. $\endgroup$ Feb 6, 2019 at 6:32
  • $\begingroup$ @Florin Maybe someone else could make a good answer to this question from the info in that Wikipedia article, but not me. ;) Ideally, an answer to this question will have some hard numbers and equations relating to the braking and heating effects. $\endgroup$
    – PM 2Ring
    Feb 6, 2019 at 9:30
  • $\begingroup$ @KeithMcClary we need to amplify the Earth's magnetic field! :-) $\endgroup$ Feb 6, 2019 at 15:39

1 Answer 1


A fixed magnetic field will induce an electrical current in a conductive object moving through the field.

No. It will induce an EMF in one direction as described in HyperPhysics. It will not induce a current since there is no return path.

This is different from induction braking, where you have a magnet with a non-uniform field moving near a conductor. It is the changing magnetic field at points within the conductor that induces the EMF and causes currents.

Alternatively, we can consider how electromagnetic fields transforn according to Relativity. If an object is moving at constant velocity through a uniform B field then, in its rest frame, it will experience a combination of uniform E and B fields which would not produce a current. (Any current would have to be due to the spacial rate of change of the field, which would be tiny on the scale of the Earth's field.)


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