Say there’s an iron nail sitting on the table and I bring a permanent magnet close enough above it that the nail comes off the table and sticks to the magnet. Now it appears a force has been exerted on the nail to move it over a distance (the definition of work, measured in units of energy). Where did the energy come from?
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The nail started out in a high energy state with respect to the magnet. Imagine a comet falling into the sun’s gravity well and getting a lot of speed, where did the comet get all that energy? It had it from the start because it started far away from the sun.
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