Can a generator and motor system create perpetual motion using Faraday's Law?

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Discussion Overview

The discussion revolves around the theoretical possibility of creating a perpetual motion system using a generator and motor setup, specifically in the context of Faraday's Law of induced electromotive force (emf). Participants explore the implications of ideal conditions, such as resistance-free wires and negligible friction, while acknowledging the fundamental principles of thermodynamics.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Dan introduces the idea of a generator powering a motor that turns the generator, questioning if this could operate indefinitely under ideal conditions.
  • Some participants assert that resistance-free wires are not achievable outside of superconductivity, and even then, other forms of resistance like friction and air resistance would prevent perpetual motion.
  • Others argue that even in a theoretical scenario with no losses, the system would not produce useful work, as all energy would be required to maintain motion.
  • One participant compares the system to a frictionless ball bearing, suggesting that it cannot exceed its initial energy state.
  • There is mention of the laws of thermodynamics, emphasizing that the best one can achieve is to break even, and that perpetual motion devices cannot extract useful energy.
  • Some participants discuss the concept of "over unity," indicating a misunderstanding of perpetual motion as seeking efficiency greater than one.

Areas of Agreement / Disagreement

Participants generally agree that perpetual motion is impossible under real-world conditions, but there is a theoretical exploration of what might happen under idealized scenarios. Multiple competing views exist regarding the implications of these ideal conditions.

Contextual Notes

Limitations include the dependence on idealized assumptions such as perfect efficiency and the neglect of real-world factors like friction and air resistance. The discussion also touches on the definitions and implications of thermodynamic laws without resolving them.

danago
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Hi. In class we are currently studying electromagnetism. The unit we are currently doing is on generators and motors using faradays law of induced emf.

While reading, i had a random thought:
If a generator is set up, such that its output current is directed to a motor, which creates rotation, which in turn is used to turn the generator coil, will the system continue to operate forever, assuming resistance free wires.

Ofcourse, the generator will have to be given an initial 'push' to get the current flowing.

Now, I am sure there must be some flaw in what I've said, or some physical problem with the setup, since as far as i am aware, perpetual motion is impossible.

Ive just posted this really for the sake of curiosity, so if anybody is able to comment on what I've said, id be greatly appreciative :)

Thanks,
Dan.
 
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To start with, there is no such thing as 'resistance-free' wires, unless you're going into superconductivity. If you can achieve that at room temperature, then you'll be so rich that nothing else matters.
More to the point, though, are things such as friction and air resistance.
No matter how you look at it, it ain't going to work.
 
Ok, that's fair enough. But I am just asking this as a theoretical question; its not like I am actually going to go and try it.

Lets say that it was possible to attain resistance free wires, and air resistance and friction etc. were negligiable. Would it work then?

Thanks for the reply btw.
 
You wouldn't get anything out of it. All the energy would have to be put back into keep the thing running. Think about a frictionless ballbearing rolling back and forth in a dish. It can never get any higher than its original starting point.

The above are statements about ideal systems with no friction and may be summarized as: "You can never do any better than breaking even."

For the case of real systems (which you don't care about) there is an even worse rule which says: "You can't even break even!"
 
You might consider that if you eliminate all air friction and mechanical friction then you don't need the wires.
The rule is that an object in motion will stay in motion until an external force acts on it.
 
I got to admit, No Time, that I never even thought of it that way. Great point!
Danago, let's review the 4 laws of thermodynamics for future reference.
1) No matter how hard you try, the best that you can do is break even.
2) You can only break even at 'absolute zero'.
3) 'Absolute zero' is impossible to attain.
4) No matter how much you shake it, the last drop always goes down your pants.
As Olgranpappy pointed out, the absolute maximum energy that you can attain under ideal conditions would be just enough to keep the system in motion. No useful work could be extracted from it. That applies to any perpetual motion device, regardless of what mechanism is involved.
 
Well anyway, yes, if you have a perfectly efficient motor and generator and no other losses of any kind, your system will not lose any energy and will run forever according to Newton's first or the law of conservation of energy...

...but that isn't a terribly useful thought experiment.
 
HTS wire will carry a current forever? that's real...
 
'High Temperature' and 'Room Temperature' are worlds apart. I'm not sure what the cut-off point is, but I think that it's something like 50°K that is considered the 'HT' boundary.
 
  • #10
Danger said:
'High Temperature' and 'Room Temperature' are worlds apart. I'm not sure what the cut-off point is, but I think that it's something like 50°K that is considered the 'HT' boundary.

thats not the point, its a real system that breaks even and btw the record for highest temperature while still SC is 135K
 
  • #11
ice109 said:
thats not the point

True. The actual point is that you can't extract anything useful from a PM device. How long would the current in your SC loop keep going if there was a light bulb in the circuit?
As to the temperature, I don't even try to keep track of what the record is. I was referring to the bottom limit of what is considered 'high temperature', and I really don't know what that is.
 
  • #12
ice109 said:
thats not the point, its a real system that breaks even...
So is an orbit. The term "perpetual motion" isn't exactly the best term to describe the issue. People looking for perpetual motion aren't actually looking for an efficiency of 1, they are looking for an efficiency > 1.
 
  • #13
Yeah. I never heard the term 'over unity' until I joined PF, but I like it.
 
  • #14
Danger said:
I got to admit, No Time, that I never even thought of it that way. Great point!
Danago, let's review the 4 laws of thermodynamics for future reference.
1) No matter how hard you try, the best that you can do is break even.
2) You can only break even at 'absolute zero'.
3) 'Absolute zero' is impossible to attain.
4) No matter how much you shake it, the last drop always goes down your pants.

Hey Danger, I've heard all of those except the 4th one. I don't get what it is saying. What does it mean?
 
  • #15
urea-related humor

hover said:
Hey Danger, I've heard all of those except the 4th one. I don't get what it is saying. What does it mean?

I can't tell from your name--are you a guy or a girl? If the latter then it might help for you to think of this one from a guy's perspective.
 
  • #16
olgranpappy said:
I can't tell from your name--are you a guy or a girl? If the latter then it might help for you to think of this one from a guy's perspective.

Is this suppose to be disgusting? If it is then don't tell me.
 
  • #17
Thanks for the bail-out, Pappy. :biggrin:
 
  • #18
hover said:
Is this suppose to be disgusting?

Disgusting only because it's true. Why do you think that guys prefer dark trousers for formal wear?
 
  • #19
Never mind then. Forget i even asked.
 
  • #20
I forget

hover said:
Never mind then. Forget i even asked.
Consider it forgotten--consider what forgotten?

... Exactly.
 
  • #21
olgranpappy said:
Consider it forgotten--consider what forgotten?

... Exactly.

:smile::smile:
 
  • #22
hover said:
:smile::smile:

Yup... he must be a girl... :rolleyes:
 
  • #23
Danger said:
Yup... he must be a girl... :rolleyes:

I just don't care to hear what it ment ok? Can you please leave it at that?
 
  • #24
No worries; I left it on the last page.
 
  • #25
Danger said:
I got to admit, No Time, that I never even thought of it that way. Great point!
I got you on one? :biggrin:
Usually, it seems the other way around. :smile:
 
  • #26
Yeah, right... :rolleyes:
 

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