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A question about magnets


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My son is revising for his GCSE mocks at the moment and this lunchtime asked me a question which I am completely unable to answer, so I thought I'd offer it to a wider audience :)

He asks: "If an object starts moving as a result of being attracted to a magnet, where has the kinetic energy gained by that object come from?  Has something else lost energy (so that energy is conserved), and if so, what, and how?"

James

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My guess would be is that it's "potential energy". When the object and the magnet were initially placed where they were, the work was done which imbued the object with said magnetic potential. Similar to climbing some stairs against gravity and stopping at the top, you imbue yourself with gravitational potential: if the stairs are suddenly removed, or a rung breaks, that energy is converted into kinetic energy.

Magnus

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4 hours ago, JamesF said:

 

He asks: "If an object starts moving as a result of being attracted to a magnet, where has the kinetic energy gained by that object come from?  Has something else lost energy (so that energy is conserved), and if so, what, and how?"

James

As Captain Magenta says, potential energy. The objects initial potential energy ( this PE being a consequence of it's initial position relative to the magnet) is converted to kinetic energy as the object 'falls' towards the magnet.

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