Has it ever actually been proven that perpetual motion is impossible ?

Question

In theory many theory's deny the possibility , however all theory is not fact until proven beyond question , accepted facts will always be subject to new theory and therefore are not un-questionable .

It seems to me that when the question of perpetual motion is raised , the only reasonable answer is "we don't know?"

Answer 1

Not many people realise this but perpetual motion is scientific fact. It's inherent in Newtons laws which state that an object will keep moving unless a force acts upon it - that force may be in the form of friction or a push or pull etc., but if none of those happen the object will move forever. You could just as easily ask "is perpetual stillness possible"?. Then the answer seems obvious - of course it is unless a force makes the object move. But without a background (posh term is a frame of reference) you can't tell whether an object is moving or not so the two statements are equivalent.

What you can't have is perpetual acceleration.

Answer 2

Okay think of Newton's Law: An object in motion will remain in that state of motion unless acted upon by some external force. The problem with "perpetual motion" is that there is ALWAYS an external force. So, the state of motion is always affected, will diminish and eventually stop. By definition, "perpetual motion" system implies one that will not need any type of maintenance or up keep or monitoring. It starts and goes on by itself forever.
To clarify a previous answerer's thought: No, the planets are not a perpetual motion system. It would take billions of years and the Sun would turn into a red giant before it happened, but the Earth will eventually degrade in its orbit and plunge into the Sun. Even the Moon is causing the Earth to spin slower and slower stretching out the length of a day. Think of what the Sun's gravitational effect is doing to the planets.

Answer 3

Think of it this way: to make something move requires some energy. Something in motion will remain in motion as long as that energy is there. The moment you begin to remove some of that energy (for example thru friction, heat, by tapping some of that energy to do some work for you) then the motion starts to slow down. Eventually all the energy required will be expended and the motion will stop. There is no way to create something that is in perpetual motion since some of its energy will begin to be expended to the rest of the universe if nothing else in the form of heat. If there was an object that was the only thing in the universe and it was in motion, then it would be in perpetual motion but, 1. of what use would that be and 2. how would you be able to tell that it was in perpetual motion since you could not be in the universe either?

Answer 4

It depends if you mean proven experimentally, or proven mathematically.

Clearly an expirement to prove that perpetual motion cannot exist would take forever.

However, the nice thing about Physics is we can test things mathematically instead of physically. As we come up with mathmatical models for the physical world we can test them. We can see if the models produce the same results as experiments do. We can also use these models to predicts results to experiments we've never performed yet. If they predictions come to be, we gain more confidence that the models are correct.

Today's mathmatical models of the universe say that what is usually called a "perpetual motion machine" is impossible. It has been proven, but it has been proven mathmatically.

One could argue that our models are wrong. But there are no serious (take that to mean what you will) physicists who believe we are wrong on this point. If you claim the models are indeed wrong then you should be prepared to provide a new model that either better fits experimental data or can make predictions that can be tested.

Answer 5

I agree with the comments above on "proving a negative" and thermodynamics.

However, if you just want something to go forever, without extracting energy, what about the electron in a hydrogen atom? In the momentum representation of ground-state hydrogen, the electron is zipping around, and in the absence of external perturbation will do so forever, as far as we know. Maybe the proton will decay eventually, but this hasn't been demonstrated. Certainly there are quite a few hydrogen atoms in intergalactic space that recombined 13.7 billion years ago, survived the period of reionization, and still have internal motion today.

Also, what if you shine a flashlight into a dark sky? Current evidence is that most of the photons will never be absorbed by anything, ever. Each photon will become less energetic as time goes on, but they'll still be streaming outward at the speed of light for the indefinite future.

Answer 6

Well there are two laws (note, laws not theories) of the universe which will prevent perpetual motion. One is Entropy. Every energy system over time will drift toward equilibrium. Second is transmission. For a system to remain perpetual, it can have no energy loss. This would require all components to work at 100% efficiency with 0% loss from friction/heat etc. A perpetual motion machine would have to be 100% perfect in every way. And in the known universe, perfection is an impossibility.

Answer 7

Actually perpetual motion means a contraption working/being in motion forever (witout being supplied with external force). This can easily be proved not possible as we have friction on earth. Every medium (except vaccum) opposes motion i.e. offers friction. Hence, any moving body will be opposed by this friction and lose some of its energy untill it eventually stops. One can argue that the lost enegy can be reabsorbed by the body as some other form of energy. But since no object is 100% efficiant it will nonetheless lose some of its energy. A perpetually moving body can be made in vaccum where no other force acts on the system (or the net force acting on the system is nil). This clearly shows that perpatual motion on Earth is impossible.

Answer 8

The burden of proof rests on those who makes the claim that perpectual motion IS possible, since that is their proposed theory. So as you've said, no theory is fact until proven beyond question, and the theory of perpectual motion has NOT been proven even once...

So the only reasonable answer is "perpectual motion is not possible yet".

PS - in actual fact, it takes energy for the Earth and the Sun to be rotating about each other, and eventually Earth orbit will decay. This is true of all objects in space.

Answer 9

If it could it would only be a novelty, it would have no practical use, since the moment you tried to take power off it, it would stop.
I suppose the nearest thing would be some sort of motor wound up by changes in temperature but this would not be perpetual motion as such. Have a look at perpetual motion on yahoo some of them are really convincing.

Answer 10

In science nothing is "impossible" and nothing can ever really be truly proven (only disproven,) however scientists will often use the term impossible to describe something that would defy the laws of physics that we belive at this point to be true. It is possibly an inaccurate use of the word but in science we have to be able to assume certain things are true (based on observation and exhausted testing) about the universe in order to be able to make predictions about it or else we would never be able to advance. A perpetual motion machine defies the laws of thermodynamics that we believe at present to be true because any time there is motion, energy will always be lost in the form of heat, in other words the entropy of the universe is always increasing.