• Question: Why is perpetual motion deemed impossible to achieve?

    Asked by bleddy to Angela, Gabriele, Karen, Maria, Shane on 19 Nov 2013.
    • Photo: Gabriele De Chiara

      Gabriele De Chiara answered on 19 Nov 2013:

      Hello bleddy! Very deep question of thermodynamics. First of all, if we define perpetual motion as the continuous motion of a particle or a system, then it is bound to dissipate because of friction, radiation and other sources of dissipation. However uniform motion a constant velocity is possible in principle according to Newton’s first law (or Galileo’s principle of inertia). However, if we define perpetual motion, a machine that given a first impulse continuously produces work without additional energy then this is impossible because of the first law of thermodynamics: all the energy must be conserved, in order to produce work we have to invest energy of some form (electricity, heat, motion from the wind of from water).

    • Photo: Karen McCarthy

      Karen McCarthy answered on 19 Nov 2013:

      Perpetual motion is the idea that an machine could continuously power itself, for example a clock could continuously wind itself.

      This is considered impossible to the 3 laws of thermodynamics, which dictate the rules of energy transfer. For perpetual motion to exist, we would need a material which generates more energy than it uses, but so far even radioactive materials have a finite amount of energy.

    • Photo: Shane Mc Guinness

      Shane Mc Guinness answered on 19 Nov 2013:

      Great question Bleddy. Yep, I’m afraid the guys are right. Energy has to come from somewhere! Having it in one place means it has come from another, no matter how many times it changes form (from light, to heat, to mass, and back again…!)

      But you’re not the first person to think about this. Did you know that Leonardo da Vinci used to think about this too!? He thought up an idea of a water wheel (like one you would see in an old flour mill along a river) which when it turned pumped the water up to the top of the mill. Then this water would fall and turn the wheel again. Seems logical right? Well, what about all that friction from the water running along the wood? Or the sound it makes? Or the heat generated? Or the work it’s doing in grinding flour? It’s all energy escaping from the system or loop. Therefore, to keep it moving it would have to generate energy from nowhere, breaking the laws of thermodynamics!