# Perpetual Motion

#### Kalrag

Alright, Ive been into the argument of perpetual mation. Ive seen the debate for each side and I wanted to see you guys thought. There is one theory that seems to prove it. If prepetual motion isnt real then why do electrons around an atom never stop?

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#### Lsos

I can't answer that question other than to say this: don't apply your everyday experiences to how an atom works. There's a whole other physics for how stuff operates at atomic scales, and simplyfying it to "an electron orbits the nucleus" will get you nowhere.

#### tiny-tim

Homework Helper
the argument is that there's no perpetual motion machine

a machine is something you can extract work from, but you can't extract work perpetually from an electron around an atom

#### Kalrag

oh well that clears it up...

#### Relay

The universe is a perpetual motion machine. Getting at all that energy is the trick.

#### HallsofIvy

Homework Helper
1. You do NOT need to extract energy in order that something be a "perpetual motion machine". All you need is that it keep moving "perpetually".

2. Electrons orbiting a nucleus is NOT a "perpetual motion machine" because electrons do NOT "orbit" the nucleus in the same way planets orbit the sun.

3. The universe is NOT a "perpetual motion machine". It will eventually suffer "heat death".

#### LeonhardEuler

Gold Member
1. You do NOT need to extract energy in order that something be a "perpetual motion machine". All you need is that it keep moving "perpetually".
That's not quite right because merely to have something moving forever does not make something a machine. It's indisputable that atoms in ordinary thermal motion in an isolated piece of metal moving forever, or photons moving out into space forever would not violate the laws of thermodynamics. There may or may not be other reasons these things are impossible, but they would have to come at least partially from outside the laws of thermodynamics. There is even a class of hypothetical perpetual motion machine that does not violate any of the laws of thermodynamics, but may or may not be impossible to build for other reasons. I wrote a long post on this here:

#### tiny-tim

Homework Helper
The universe is a perpetual motion machine. Getting at all that energy is the trick.
No, getting the work out is the trick

where would it go?
Ive seen the debate for each side …
There is another side?
The debate is a perpetual motion machine!

#### Relay

Isn't energy the ability to do work? Batteries, springs, flywheels, etc. have energy because they can do work. When they can no longer do work, they have no more energy left.

#### Dr Lots-o'watts

The debate is a perpetual motion machine!
(I thought those three words were taboo in these parts!...)

#### LeonhardEuler

Gold Member
Isn't energy the ability to do work? Batteries, springs, flywheels, etc. have energy because they can do work. When they can no longer do work, they have no more energy left.
Actually, it isn't. Energy is conserved, but the ability to do work is not. For instance, suppose you have a book that you have lifted. Because it is some height above the ground, it has potential energy. This can be converted to work, for instance by lifting another weight with a pulley. Suppose, however, you just drop the book. As it falls, this potential energy is converted to kinetic energy. You can still convert this to work, for instance by having it land on one end of a catapult-like device.
But suppose, instead it just lands on the floor. This energy is now mostly converted to heat. Some is converted to sound, but this too is eventually dissipated to heat due to viscous effects in the air. The sound can also be minimized by having the ground be clay, or some other soft, non-rubbery material. The temperature of the ground is raised slightly. Can this be used to do work?

Somewhat. If you have something colder than the ground to accept the heat, then you can build a heat engine. But you will never get back all of that energy. Some of it will necessarily be wasted. The laws of thermodynamics imply that the maximum efficiency with which heat can be converted to work is:
$$\frac{T_h - T_c}{T_h}$$
where T_h is the temperature of the hotter body and T_c the temperature of the colder one, both measured on an absolute scale (0 needs to mean absolute 0). This is called the Carnot efficiency. The 2nd law of thermodynamics implies that every heat engine must have two reservoirs at different temperatures. From this you see that the only way to get 100% efficiency is with a cold reservoir at absolute 0 or a hot reservoir at infinite temperature. But infinite temperature is not possible, absolute 0 is probably impossible, and as soon as you started a machine with a reservoir at absolute 0, it wouldn't be at absolute 0 anymore because it just absorbed heat.

So heat and work are different forms of energy. You can go from work to heat at 100% efficiency, but not the other way around.

#### RonL

Gold Member
Re: Work and Heat

Having seen many comments recently that work can be converted to heat 100%, but heat cannot be converted to work in the exact proportion, as stated by Rudolph Clauisus. Has his statements to the heat/work equality been discarded ?

I believe 100% cannot be exceeded, what law states it cannot be reached ?

Gold Member

#### RonL

Gold Member
Re: Work and Heat

The Second Law of Thermodynamics, most directly the Kelvin statement of the law:

"No process is possible in which the sole result is the absorption of heat from a reservoir and its complete conversion into work."
http://en.wikipedia.org/wiki/Second_law_of_thermodynamics#Kelvin_statement

http://en.wikipedia.org/wiki/Compressed_air_energy_storage

"Isothermal processes are thermodynamically reversible. To the extent the compression process is isothermal, its efficiency approaches 100%.[12] The above equation represents the maximum energy that can be stored. In practice, no process is perfectly isothermal and the compressors and motors will have heat-related energy losses".

A quote from wiki that I found as a result of jimgram's threads about flywheels. I have been having a hard time deciding if making a thread in the engineering section is what I really want to do, in regard to a design that brings heat in with air and has greater thermal ability than losses in the bearings and air friction on the exposed surfaces.

OmCheeto linked this a couple of years ago in a discussion on flywheel storage, but it went unnoticed by me.

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#### LeonhardEuler

Gold Member
You raise a good point, which is why the actual statement of the 2nd law says
"No process is possible in which the sole result is the absorption of heat from a reservoir and its complete conversion into work."
When a gas expands, it's entropy increases. This entropy increase can allow the conversion of heat into work if the two processes are coupled, so that the overall entropy change is positive or 0. This is why some other statements of the 2nd law refer to cyclical processes.

#### RonL

Gold Member
You raise a good point, which is why the actual statement of the 2nd law says
"No process is possible in which the sole result is the absorption of heat from a reservoir and its complete conversion into work."
When a gas expands, it's entropy increases. This entropy increase can allow the conversion of heat into work if the two processes are coupled, so that the overall entropy change is positive or 0. This is why some other statements of the 2nd law refer to cyclical processes.
I have in the past, on a number of occasions tried to explain different designs, but have always confused things by trying to include too much information on the extra things that can add to the transfer process.
I have almost always suggested very fast cycles that do not draw down the speed of flywheels in motion.

#### Relay

So thermal energy is the exception and not the rule? You can convert electrical energy with 100% efficiency to heat, but never the other way around. So is energy not conserved when it is in thermal form?

#### LeonhardEuler

Gold Member
It's not an exception to conservation of energy, it's just the form of energy that other energy tends to wind up turning into, but tends not to turn into other forms.

#### Relay

So the universe is destined to die of thermal equalibrium. What about the new theories suggesting that black holes shoot out matter at their poles. See "http://www.youtube.com/watch?v=gib2i3_KW5Y&feature=related". Wouldn't the disturbances caused by those processes prevent thermal death of the universe?

#### ZapperZ

Staff Emeritus
2018 Award
Please note that valid references to be used in this forum are not YouTube videos, but either established texts or peer-reviewed journals.

Zz.

#### pallidin

Please note that valid references to be used in this forum are not YouTube videos, but either established texts or peer-reviewed journals.

Zz.
I would agree. YouTube videos can be entertaining and possibly informative. Yet, one has to careful about their authenticity/legitamacy.
Not saying that ALL YouTube science related videos are bunk. For example, there are some excellent MIT lecture series available on YouTube.
Apart from that example, I always approach YouTube "science" videos as a sceptic.

#### Relay

Youtube is just a media for information exchange. The MIT lectures are very educational, I agree. The NASA water sphere experiments are mind blowing.(Bubbles going down instead of up.) However, I was just pointing to one video which suggested that black holes release matter. My previous understanding of black holes was that nothing escaped from one, not even light. This video suggests otherwise. I believe that there might be some truth in the video. Then again it could all be bull. I presented the video not as proof, but as the reason for my present thoughts. So do black holes release matter or don't they?

#### jimimick

Alright, Ive been into the argument of perpetual mation. Ive seen the debate for each side and I wanted to see you guys thought. There is one theory that seems to prove it. If prepetual motion isnt real then why do electrons around an atom never stop?
I guess if u take a single atom with a single electron the electron spinning round has no resistance to its motion and is basically in space so therefore it wouldn't slow down but just keep going, almost like the moon moving around the Earth.

My theory ****s up when u have 2 or more atoms side by side because the if the electrons were sniping in opposite directions the opposing charge would slow them down. I suppose that repulsion charge would give each atom kenetic energy which would then be changed back into energy somehow....

#### aac70

wow I am glad I joined this site however from the completely dumb level I come from I can almost see how this argument can be solved "proof" all the big names I have spoken to about this all say it cant be done because of this and that and the other thing but none of them talk about the use of potential energy and how it can be used in a way to over come the energy loss through friction can some one help me out with this one please???

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