What is wrong with a perpetual motion machine?

  • #36
krab
Science Advisor
893
3
bino said:
sorry i used the wrong analogy a magnet does work by pulling metal toward it.
i am wrong about it just sitting on the fridge.
You are (now) quite right. But what has this to do with Perpetual Motion?
 
  • #37
omin
187
0
The_Thinker said:
I'm just curious, why is it that anye perpetual motion machine that is thought up is discarded immedietly. I know that energy can't be created nor can be destroyed but then again, a few centuries we were absolutely positively sure that the Earth was flat! I mean anything can be wrong, why Newton's law's itself was proved wrong and we still learn them in school! How can we be so sure that it can't possibly work! Can someone clear this out for me?

You can't prove a theory like Newtons wrong. You may only present a theory that is more correct and thereby showing how it is less accurate. But Newons laws present the very fundamentals that we use to quantify, so it will never be proven wrong, unless you give up comparison and counting in general itself. Without those two things, which are at the heart of his laws, you can't anthying sensable to humanity.

If you are patient and study all those laws, it will bring you to the energy concept. You'll learn about the different forms energy takes. When you account for all these forms, you'll begin to see what it means. It gets clearer and clearer as you go further.

Lets humor ourselves and say we created a perpetual motion machine. It would be a machine that would have motion for ever right? This means a machine must have motion, but no force can act upon it. That would mean it would move perpetually.

We make the machine. It's two mirror with a few photons bouncing back and forth. The photons stay in the mirrors perfectly. No outside force acts upon the photons or the mirrors. That's a perpetual motion machine.

What happens when you try to use some of the energy? You must take out a packet of energy. This means a force must acts upon your perpetual machine.

To grab a photon from your machine, you must exert a force upon your machine. Once you exert a force upon it you are exerting energy upon the machine.

So how does any machine ever give energy perpetually if first a force must act upon it to get energy from it?

______________________________
Nothing happens without a collision.
 
  • #38
bino
180
0
if someone were able to make some kind device that could harness that pulling or pushing of magnets then we could get a perpetual machine.
 
  • #39
krab
Science Advisor
893
3
So now you no longer believe the Makar quote you gave in post 31?
 
  • #40
Mk
2,037
4
Nah, magnets run out of power, it takes a while, but yes they do.

Where do electrons get their constant orbital motion from? In superconducters how does electricity flow without resistance? Superfluidity, how do superfluids flow without friction? In the quantum world, their is no friction?
 
  • #41
The_Thinker
146
2
Magnets lose their properties eventually... This i did not know, is it true...?
 
  • #42
krab
Science Advisor
893
3
Magnets may eventually lose their field, but that is entirely beside the point. The point is that the field is conservative. That means it takes a certain energy to set up a configuration of separated magnet and paper clip (e.g.). You get some of that energy back when the paper clip moves toward the magnet, but then you'll have to input the energy to separate them again. This is essentially how a motor works. Costly electrical energy in, mechanical energy out. There is no free lunch and no PPM.
 
  • #43
bino
180
0
but if you were able the set them up in such a way so that the magnets are always being pushed or pulled for as long as the magnets have they power. then you could get free energy. granted is would not be forever because magnets don't last that long but it would be a long time.
 
  • #44
krab
Science Advisor
893
3
bino said:
but if you were able the set them up in such a way so that the magnets are always being pushed or pulled for as long as the magnets have they power. then you could get free energy.
What you are saying makes no sense. Imagine you have a big magnet on a truck, attracting a vehicle behind you. It's true that this vehicle can get an infinite number of miles per gallon. But the truck gets corresponding worse mileage. Magnetic fields are not some kind of magic. It would operate in exactly the same way as if the vehicle were being pulled by a rope. You are essentially saying that if you connect a number of masses with ropes with stored energy (OK, say bungee cords), then you think it's possible to invent a configuration where all the masses move forever. OK now the concept seems silly doesn't it?
 
  • #45
rayjohn01
283
0
Electrons , neutrons ,protons etc ARE perpetual motion machines , left undisturbed they will continue what they are doing forever -- however they do NO work.
Work means extra motion over and above whatever the system had to begin with -- where can this come from -- only outside the system . for an isolated system work in means work gained ( no gain from within ) usually not 100% efficient except in atomic systems. There is no mystery here it is all a matter of motion and the concept ( deep enough) of the conservation of motional energy and momentum.
The question you should ask is why do you wish to deny ordinary physics , it appears to me that there is a deep seated desire to get something for nothing -- why ?
 

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