Understanding Energy and Magnetism: Debunking Common Misconceptions

[HummusAkemi]

I pry two magnets apart. The magnets attract each other. Say they exert a constant force F on each other. I exert an equivalent force F on each in the opposite direction and pull them apart a distance d (pull each of them d/2 distance). So I have done positive work Fd in total and increased the potential energy of the arrangement by Fd. The magnets have each done negative work -Fd/2 on each other.
Me: lost Fd energy
Left magnet: lost Fd/2 energy from work done on other magnet
Right magnet: lost Fd/2 energy from work done on other magnet
The potential energy of the arrangement rose by Fd.

Anyone tell me where I messed up? Because conservation of energy doesn't work out.

 

[Simon Bridge]

The magnets have not lost any energy - you have done work storing energy in the magnetic field between the magnets.
The amount of energy stored is the same as the work you did.

 

[Delta2]

Τhe middle statements about the left and right magnet are wrong. The left magnet doesn't lose Fd/2 energy instead it gains Fd/2 potential energy. Similar right magnet gains Fd/2 potential energy. It is a gain in potential energy rather than a gain in kinetic energy that we would have if there was no magnetic field. You view that "possible" gain in kinetic energy as a loss which isn't really an energy loss, it is a gain in potential energy instead.

 

[HummusAkemi]

Thanks, you two. Ok, I think I get it now