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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If you’re worried about conservation of energy, don’t be. In order to exploit the magnet for energy, you need to separate the nail from the magnet before the magnet it able to pull on it again. So yes, work is done to pull the nail towards the magnet, but then you apply work and energy to separate them. In the end, we have not stumbled on an unlimited energy scheme. Darn!
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