Why doesn't the buoyant wheel and belt perpetual motion machine work?

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Discussion Overview

The discussion revolves around the reasons why a buoyant wheel and belt perpetual motion machine does not function as intended. Participants explore theoretical and conceptual aspects of buoyancy, energy conservation, and the mechanics involved in such machines.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants suggest that the conservation of energy is the fundamental flaw preventing the machine from working.
  • Others argue that it is possible to demonstrate the machine's failure without directly invoking conservation of energy, indicating that energy loss occurs somewhere in the system.
  • A participant points out that buoyancy operates similarly to gravitational potential energy, where energy is required to return a system to its original state.
  • One participant discusses the resistance encountered when pushing air down, which is compared to the resistance faced when pushing buoyant objects into deeper water.
  • Another participant raises the question of whether increasing the size or number of cups in the machine could enhance its performance, suggesting that this might not resolve the underlying issues.
  • Some participants reflect on the historical context of patents for perpetual motion machines, questioning the rationale behind their approval.
  • A later reply emphasizes that increasing the size or number of cups would also increase the counteracting forces, thereby not solving the problem.

Areas of Agreement / Disagreement

Participants generally agree that the conservation of energy plays a crucial role in understanding why the machine fails, but there is no consensus on the specific mechanisms or explanations for the energy loss involved. Multiple competing views and interpretations remain present throughout the discussion.

Contextual Notes

Participants express uncertainty regarding the specific mechanisms of energy loss and the implications of buoyancy in the context of the machine's design. There are unresolved questions about the effectiveness of modifications to the machine.

myanmar
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perhaps you can help me.
on http://www.lhup.edu/~dsimanek/museum/themes/buoyant.htm fundamentally, what is the reason that the picture under the words "buoyant wheels and belts" doesn't work? (Except remove the movement of water between two buckets. replace that with compressing and expanding air)
 
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The last paragraph on that page wasn't clear? What was confusing about it?
 
That almost sounds like saying
"It won't work because of the conservation of energy".
which I understand.

I just don't see where the flaw is that makes it stop working.
 
But conservation of energy is the flaw that makes it stop working.
 
While this is certainly true, we should be able to prove this without relying on the conservation of energy.

That is, there is somewhere in the system where energy is lost or something I have ignored.
 
myanmar said:
While this is certainly true, we should be able to prove this without relying on the conservation of energy.

That is, there is somewhere in the system where energy is lost or something I have ignored.
Can you prove you were driving under the speed limit without citing the speed limit?

Conservation of energy isn't just a law that we go back and check to see if it was violated after doing a problem, it is a tool used to do problems. When doing a problem like this, you write a conservation of energy statement: Eout - Ein = 0 ...and see if it works.
 
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The point is that you don't need to lose energy. You show that when you move the machine from one position to the next and you recover the same configuration. The energy must be the same (ignoring dispersive forces), so you can't extract energy out. When you include dispersive forces - any ones, anywhere - it can only act to slow things down.
 
That said, it can be interesting to analyze in detail how such a machine actually behaves, and where exactly it doesn't behave as its inventor claims. Analysing PMM *can* be fun. I think that was what the OP was asking for.
 
There is nothing magical about buoyancy, it is fundamentally no different than rolling a rock down hill. Both cconvert gravitational potential energy into work. When you go to roll the rock back up the hill it takes at least as much energy as you got out. In buoyancy the "rock" is the fluid. Rolling it downhill can give you work (like a water wheel) but as soon as you try to roll it back uphill you lose all of the energy and more.
 
  • #10
vanesch said:
That said, it can be interesting to analyze in detail how such a machine actually behaves, and where exactly it doesn't behave as its inventor claims. Analysing PMM *can* be fun. I think that was what the OP was asking for.

Of course, the committed (and I mean committed) inventor may just change a few details and say "OK, now it'll work!"
 
  • #11
myanmar said:
I just don't see where the flaw is that makes it stop working.

Irreversibilities.

CS
 
  • #12
Perhaps the mechanism you are looking for is the buoyancy of the air that must be forced down from the piston at the top of the belt to the piston at the bottom. This buoyancy can be understood as the difference in water pressure between the top of the belt and the bottom. In order for the topmost piston to push in, the lowest piston must be forced to expand. However, this lowest piston will resist expansion due to this difference in pressure. This is the same resistance encountered any time one tries to push air (or any buoyant object or substance) downward into deeper water.

This resistance will be equal to the rotational force supplied by the overall process. Since the two forces are equal and opposite, the machine remains still.

Is that the sort of answer you are looking for?
 
  • #13
I did like the fact that the machine in the link was patented - in 1976!
I can understand the patents from 18xx when perhaps the patent office wasn't quite as stocked with greatest minds of it's generation and technical education was a little lacking.
But 1976 - surely they must have had a memo with "Remember no perpetual motion machines" by then!
 
  • #14
mgb_phys said:
...
I can understand the patents from 18xx when perhaps the patent office wasn't quite as stocked with greatest minds of it's generation...

I think back then we didn't have those volumes of useless patent applications. Today they don't really care if it works, because then there will be no claims either.
 
  • #15
LURCH said:
Perhaps the mechanism you are looking for is the buoyancy of the air that must be forced down from the piston at the top of the belt to the piston at the bottom. This buoyancy can be understood as the difference in water pressure between the top of the belt and the bottom. In order for the topmost piston to push in, the lowest piston must be forced to expand. However, this lowest piston will resist expansion due to this difference in pressure. This is the same resistance encountered any time one tries to push air (or any buoyant object or substance) downward into deeper water.

This resistance will be equal to the rotational force supplied by the overall process. Since the two forces are equal and opposite, the machine remains still.

Is that the sort of answer you are looking for?

LURCH, this is exactly the kind of answer I'm looking for.

However, wouldn't adding more cups (or making them bigger) increase the rotational force and make this irrelvant?

If not, explain.
 
  • #16
I can understand the patents from 18xx when perhaps the patent office wasn't quite as stocked with greatest minds of it's generation and technical education was a little lacking.

Yes, and by 1902 there was that German chap working in the Berne Federal Office for Intellectual property who obviously couldn't concentrate on the matter in hand.
 
  • #17
Mapes said:
Of course, the committed (and I mean committed) inventor may just change a few details and say "OK, now it'll work!"
What happens here is the same every time: the "committedd inventor" increases the complexity of the device until he/she is no longer able to analyze/evaluate what is happening, and then assumes incorrectly, "OK, now it'll work!"
 
  • #18
myanmar said:
However, wouldn't adding more cups (or making them bigger) increase the rotational force and make this irrelvant?

If not, explain.
Of course not. More or bigger cups means more work is required to push the air down (and lift the water up).
 
  • #19
myanmar said:
LURCH, this is exactly the kind of answer I'm looking for.

However, wouldn't adding more cups (or making them bigger) increase the rotational force and make this irrelvant?

If not, explain.


LOL! I know; a lot of these devices look like, "just gimme some time to work on it. If I make the weights heavier, or the air pockets larger, I'm sure I can get it to work." Sadly, however, anything you do to increase the force also increases the counterforce. For example; if you made the cups twice as large, you would double the surface area on which pressure is acting against the cup at the bottom of the belt. This of course would double the buoyant force preventing you from moving air downward (or you could say it doubles the amount of air we're trying to push down into deeper water). Using twice as many cups would have the exact same effect.
 

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