Where does the power dissipate ?

[Externet]

An electric motor spins a disc with magnets attached. Takes say 10 Watts.

 

Magnets are placed fixed near the disc.

 

The motor exerts extra effort to overcome the magnets that try to brake the disc motion. Motor takes now say 20 Watts to run overcoming the magnetic braking effect.

 

Do the magnets warm up?

 

If it was a free running drill using 10 Watts, comparing to 20 Watts when actually drilling, are the extra 10 Watts shown as heat at the drilling friction action (bit, part drilled) ?

[swansont]

Heating of the motor's wires, I'd say. The external magnets represent an additional load, or effectively a larger impedance.

[Mr Skeptic]

I think the metal disk would warm up, due to induced electric currents in it. Incidentally, that is also what limits space launches from a launch loop.

 

I don't know if the magnets themselves would warm up though.

[Externet]

Hi, Skeptic.

Metal? Say the disc is not metal. The extra effort exerted by the motor is due to overcoming the attraction/repulsion from the magnets proximity.

 

In other words, If a solenoid with a long rod had to pull a magnet away from another; compared to no magnets to act upon...

 

Separating stuck magnets does need a force x distance ÷ time

[Mr Skeptic]

Ah, well the magnets require energy to separate, true, but since it rotates eventually they get back together, for a net loss of no energy. I'm sure there would be some electromagnetic losses somewhere though -- the stationary magnets could induce a current in moving conductors such as the wires in the motor, for example. Or, the moving magnets could induce a current in stationary conductors; even far away ones would have a little tiny effect.