• Question: How is perpetual motion possible?

    Asked by to Thomas, Saiful, Piers, Meggi, Laurence, Karl, Javier, Chris on 9 Jan 2017. This question was also asked by .
    • Photo: Chris Eames

      Chris Eames answered on 9 Jan 2017:

      It is not possible because it would violate the first and second laws of thermodynamics. On a practical level you would have to put energy in to get the motion started. Then some energy would be lost due to friction, air resistance, sound etc and you would keep having to add in more energy to keep it going.

      So if you can come up with a machine that keeps going once you set it away you would be the most famous scientist of the century because you would prove all these fundamental theories and centuries of practical experience wrong ;o)

    • Photo: Piers Barnes

      Piers Barnes answered on 9 Jan 2017:

      You could hypothesise ‘perpetual’ motion of something like a rock traveling through space, as long as it doesn’t interact with anything else (i.e. no energy exchanged with the surroundings) then in principle one could imagine the motion to be perpetual. In practice the rock would interact with light from the surrounding stars, and the elements in the rock might eventually start to decay so the motion wouldn’t be truly perpetual, and the 2nd law would win in the end.

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