system
Given the following post, respond as if you're commenting on Reddit:
human
When a magnet attracts a piece of metal upwards, where does the energy come from?

Let's say I have a piece of metal on a table and I hold a magnet over it so that the piece of metal is attracted upwards. It has increased its potential energy, but where did that energy come from?
gpt
The best way to understand this is to reverse the process.  Say you have a magnet holding an iron bar over a table.  With your hand you pull the bar off the magnet and put it down on the table.  Where did the energy to do that come from?  From you.  You stored energy in the system by separating the metal from the magnet, putting the combined magnet+bar at a higher potential (with respect to the magnetic field) than it was before.  If you let the magnet get close enough to the metal to pick it up again, you're just releasing that energy that was stored there, and putting the system back at a lower potential (wrt to the magnetic field.)  Or alternatively, you're trading energy between being stored as gravitational potential and magnetic potential.