Let's say I have a bullet flying by a magnet, the magnet will attract the bullet and change its trajectory so it will turn slightly. Does that trajectory change take energy? If it does, where does it come from? The kinetic energy of the bullet?
If the magnet is bolted to the earth, then the Earth's motion may change slightly. But since the earth is much more massive than the bullet, the change will be barely noticed.
He did answer your question. In the first case the energy comes from the Earth. There is a force applied through a small distance (the change in the Earth's position and/or rotation), which is equivalent to the work done to change the trajectory of the bullet.I understand that there are forces at play there. I'm asking about energy, see my OP.