2

We all know the concept behind Perpetuum Mobile.

Instead of trying to grasp the impossible, how near could we actually approach the general idea?

By this I mean to look at the "apparent perpetual motion machines" such as the Drinking bird, Capillary Bowl, Crookes Radiometer, and so on.

These things work on a principle to take a little energy kick, and then to stay in motion for a long period of time making them look like they will go on forever, but not really.

We can even look at the planets and their orbits as a example of a apparent perpetuum mobile, since they will stay in this motion for a very long time, but not forever.


My question is, what is the colsest thing we can achieve?

In other words, a machine (a system) that will stay for the longest possible time in motion, with as little as possible energy needed?
(Preferably, longest time spent in motion after tiniest possible starting energy kick)

I'm looking for examples either possible in theory obeying the laws of physics or in real life already built examples that can be maybe even more enhanced to prolong their time in motion or reduce their energy consumption.

What is the best thing we can achieve, or think of possibly achieving so far?


In other words, how far could we actually get with a machine spending $t$ time in motion while spending a total of $E$ amount of energy if $t$ approaches $\infty$ and $E$ approaches $0$?

Vepir
  • 157
  • In theory the aim would be to create a system with high inertia and extremely low friction. A flywheel for example. – Jaywalker May 26 '16 at 13:05
  • In practical terms, what's the most efficient machine we could build? A bike or a carnot engine come closest, far as I can think of, but this might be an opinion based question. –  May 26 '16 at 13:05
  • I do however think that this question is not appropriate to the physics forum but possibly engineering. – Jaywalker May 26 '16 at 13:06
  • Theoretical engineering is of physical considerations. Most things are. Don't be snooty and push things that aren't esoteric out of your realm. – user273872 May 26 '16 at 15:50
  • "My question is, what is the colsest thing we can achieve?" I'm not sure if you meant coolest or closest there XP – user273872 May 26 '16 at 15:52

1 Answers1

3

You have the wrong idea of a perpetual machine, it is not one that keeps moving in absence of friction. You also need to be able to extract work from it after some cycle. Because of that, planets orbiting around a star do not qualify as a perpetuum mobile.

Theoretically the most efficient real machine can be at the most as efficient as the Carnot machine.