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Questions tagged [perpetual-motion]

Perpetual motion describes "Motion that continues indefinitely without any external source of energy; impossible in practice because of friction." It can also be described as "the motion of a hypothetical machine which, once activated, would run forever unless subject to an external force or to wear". There is a scientific consensus that perpetual motion in an isolated system would violate the first and/or the second law of thermodynamics.

Perpetual motion describes "Motion that continues indefinitely without any external source of energy; impossible in practice because of friction." It can also be described as "the motion of a hypothetical machine which, once activated, would run forever unless subject to an external force or to wear". There is a scientific consensus that perpetual motion in an isolated system would violate the first and/or the second law of thermodynamics.

Source: http://en.wikipedia.org/w/index.php?title=Perpetual_motion&oldid=492584324

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Why can't I do this to get infinite energy?

I know that I cannot do this because of conservation of energy, so I am looking for an answer as to why this will not work. So by my understanding of Einstein's whole famous $E=mc^2$ thing it is possible to turn matter into energy, and energy into…
Me2
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Why doesn't this perpetual motion machine using the buoyant force work?

I realize this isn't possible, but I can't see why not, especially if you change the model a little bit so that the balls simply travel through a tube of water on the way up, rather than exactly this model. Please be clear and detailed. I've heard…
Martin
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How is it possible to know a proposed perpetual motion machine won't work without even looking at it?

It is often said that perpetual motion is impossible. Many people try to invent perpetual motion machines. Apparently every such attempt is doomed to failure. People don't even need to look at one to know this. What is it about perpetual motion that…
mmesser314
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What prevents this magnetic perpetuum mobile from working?

As a child, I imagined this device, which may seem to rotate indefinitely. I have two questions. Is this perpetual motion machine already known? If it is, could you please give some references? What is the exact mechanism that makes it stop? By…
Cristi Stoica
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Can magnets rotate infinitely?

There are many videos on youtube in which people arranged magnets in circle and rotated one placing in middle of that circle on a shaft, and the magnet (magnet motor) starts madly and continues its movement. Do they really rotate infinitely? If so,…
SMUsamaShah
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Can we use the stored gravitational potential energy of a building to produce power?

There are skyscrapers sitting and pushing on the ground with tremendous weight. Is it possible to convert this weight/force to harness energy to power the building? Maybe build the building on top of some type of pendulum that will rotate under the…
Grasper
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Besides the 2nd law of thermodynamics, what laws of optics prevent the temperature of the focal point of lens from being hotter than the light source?

I'm pretty sure that you can't take a magnifying glass and make it focus to a point that is hotter than the surface of your light source. For example, when you're outside trying to fry ants with your magnifying glass, it's impossible to get it…
Griffin Teller
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Can someone explain the science behind MIT's 230% efficient LEDs?

I was reading Gizmodo the other day and I didn't quite understand the Physics behind this. Could anybody shed some light on how this effect actually works?
Kian
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Why doesn't this magnetic perpetual motion machine work?

I know that this machine does not work, via thermodynamics. I am asking for an analysis in terms of mechanics and magnetism. Anyway, so here is the machine: (source: cabinetmagazine.org) The magnet (the red ball) pull the ball up the ramp, and…
Christopher King
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How to understand Feynman's reasoning about perpetual motion?

I'm studying Feynman's Lectures on Physics, and I'm not really understanding his reasoning here: Consider weight-lifting machines $\overline{}$ machines which have the property that they lift one weight by lowering another. Let us also make a…
Gold
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Why does this perpetuum mobile not work?(Gases and Densities)

I recently came up with the following concept. It is very simple, and may have been thought of before. A picture says more than a thousand words, so here is it explained in a picture: Note that water was used to make the example easier to…
Qqwy
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Perpetual motion machine of the second kind possible in nano technology?

First of all sorry for my English - it is not my native language. During my engineering studies at the university the thermodynamics professor told us that the "second law of thermodynamics is not true for a low number of molecules". At that time…
Martin Rosenau
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Why can't we make a perpetual motion machine by using a magnet to pull up a piece of metal, then letting it fall back down?

Obviously, a perpetuum mobile isn't possible by any law in physics, because energy can't be "created" or "destroyed", only transformed. This said, I've had an idea for a perpetuum mobile and can't seem to find my mistake (I'm actually very close to…
Florian Claaßen
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Why doesn't this perpetual motion machine using magnets work?

See image: If I'm not totally dumb the car would move when the right magnet would not be attached to the car, at same distance of the booth magnets. So why would it not move?
iceteea
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Why doesn't the gravitational energy in this system of evaporating and condensing water violate the second law of thermodynamics?

Let's consider the following system shaped as in the picture below, in which the only fluid contained is water at room temperature. As far as I understand, the water should be in an equilibrium between its liquid and gaseous phases. While some of…
Will
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