Perpetual Motion: Exploring Faraday's Law of Induced EMF

In summary, Dan said that a generator set up to turn a motor will never generate enough energy to keep the system running, even if the wires are 'resistance-free'. He also mentioned that friction and air resistance are major factors in stopping the system from working.
  • #1
danago
Gold Member
1,123
4
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.
 
Physics news on Phys.org
  • #2
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.
 
  • #3
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.
 
  • #4
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!"
 
  • #5
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.
 
  • #6
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.
 
  • #7
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.
 
  • #8
HTS wire will carry a current forever? that's real...
 
  • #9
'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.

:rofl::rofl:
 
  • #22
hover said:
:rofl::rofl:

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:
 
  • #27
Ok, then - looks like we're done here...
 

1. What is perpetual motion?

Perpetual motion is a hypothetical concept of a motion that continues indefinitely without any external energy source. It is often referred to as a machine that can run forever without ever stopping or needing additional energy.

2. Can perpetual motion be achieved?

No, perpetual motion cannot be achieved. This is because it goes against the fundamental laws of physics, specifically the Law of Conservation of Energy, which states that energy cannot be created or destroyed, only transferred from one form to another.

3. How does Faraday's Law of Induced EMF relate to perpetual motion?

Faraday's Law of Induced EMF states that a changing magnetic field can induce an electric current in a conductor. This is significant because it shows that energy can be transferred from one form to another through electromagnetic induction, but it does not create new energy. Therefore, it does not support the concept of perpetual motion.

4. Are there any real-life examples of perpetual motion machines?

No, there are no known examples of perpetual motion machines that actually work. Many inventors have attempted to create such machines, but they have all failed due to the laws of physics.

5. Why is the study of perpetual motion and Faraday's Law important?

The study of perpetual motion and Faraday's Law is important because it helps us understand the fundamental laws of physics and the limitations of energy. It also has practical applications in various technologies, such as generators and motors, that rely on electromagnetic induction for their function.

Similar threads

Replies
9
Views
1K
Replies
3
Views
1K
Replies
17
Views
985
Replies
1
Views
1K
  • Introductory Physics Homework Help
Replies
7
Views
210
  • Electromagnetism
Replies
20
Views
1K
Replies
8
Views
1K
  • Introductory Physics Homework Help
Replies
11
Views
1K
Replies
13
Views
3K
Replies
27
Views
1K
Back
Top