# Do magnets lose strength by pulling them apart?

• YoungPhysicist

#### YoungPhysicist

When two magnets already sticked to each other being pulled apart, energy is applied, so I assume that the energy is stored like some sort of potential energy which will be turned back into kinetic energy when they accelerate towards each other to stick back together. So the magnet itself doesn't lose or gain anything.

But few days ago,I found that when I toss a smaller magnet pass a larger magnet with the correct speed, distance and angle, the path of the smaller magnet will be curved by the larger one but not actually colliding into it. The event itself must have used energy, right? So where did the energy come from? Does that mean the larger magnet is actually spending its own energy,or I'm wrong at the very beginning?

Dale

The event itself must have used energy, right? So where did the energy come from?
Changing the angle at which something travels does not necessarily use energy. A force applied at right angles to the direction of motion does no work because there is no motion in the direction of the applied force.

However, it is true that a bit of energy is lost when conductive magnets pass by one another. The changing magnetic fields induce eddy currents in each other. The energy for this comes from the person that tossed the magnets past one another. [It is, more or less, the same effect that is used in electric generators].

YoungPhysicist
The reason why no work is being done is that the magnet PULLS the other magnet towards it and not away from it. Is that correct?

...but not actually colliding into it.
Why do you think this would make any difference compared to your first paragraph? If it speeds up by getting closer, it trades PE for KE, and in reverse when it passed the closest approach.

YoungPhysicist
When two magnets already sticked to each other being pulled apart, energy is applied, so I assume that the energy is stored like some sort of potential energy which will be turned back into kinetic energy when they accelerate towards each other to stick back together. So the magnet itself doesn't lose or gain anything.

Correct.

But few days ago,I found that when I toss a smaller magnet pass a larger magnet with the correct speed, distance and angle, the path of the smaller magnet will be curved by the larger one but not actually colliding into it. The event itself must have used energy, right? So where did the energy come from? Does that mean the larger magnet is actually spending its own energy,or I'm wrong at the very beginning?

See paragraph 1!

By curving towards the large magnet it gets closer than it was. So one of the magnetic potential energy is used up.

Consider this paragraph...

When two masses already sticked to each other by gravity being pulled apart, energy is applied, so I assume that the energy is stored like some sort of potential energy which will be turned back into kinetic energy when they accelerate towards each other to stick back together. So the mass itself doesn't lose or gain anything.

Look familiar?

What happens when a space rock flies past a planet?