Feynman: Reversible machines, no perpetual motion?

In summary, the author discusses the concept of perpetual motion and how it is not possible in reality. He defines perpetual motion as a machine that does work without needing any input from an external force. The author also states that this is not what defines a perpetual motion machine, and that a machine must do work in order to be considered a perpetual motion machine.
  • #1
SchroedingersLion
215
57
Greetings,

I have begun reading the Feynman Lectures to repeat the most important ideas from my undergraduate studies and to improve my intuitive understanding of physics.

In one of the first chapters, the one about the conservation of energy, he demonstrates that the conservation of energy is equivalent to the statement that there can be no perpetual motion.
Even an ideal (=reversible) machine can not drive an external motion perpetually under the assumption of conserved energy (and vice versa, under the assumption of no perpetual motion, energy is conserved in that reversible machine).

What I am asking myself is: Isn't a reversible machine in itself not a possibe perpetual motion?
He defined perpetual motion with respect to an external object that moves because its driven by the machine.
But what about the machine itself? It can go from A to B, but also from B to A without the need of energy since it is reversible. In principle, if reversible machines existed one should be able to design one that moves perpetually like A-->B-->A-->B-->A...

What am I missing?

Regards
 
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  • #2
SchroedingersLion said:
Greetings,

I have begun reading the Feynman Lectures to repeat the most important ideas from my undergraduate studies and to improve my intuitive understanding of physics.

In one of the first chapters, the one about the conservation of energy, he demonstrates that the conservation of energy is equivalent to the statement that there can be no perpetual motion.
Even an ideal (=reversible) machine can not drive an external motion perpetually under the assumption of conserved energy (and vice versa, under the assumption of no perpetual motion, energy is conserved in that reversible machine).

What I am asking myself is: Isn't a reversible machine in itself not a possibe perpetual motion?
He defined perpetual motion with respect to an external object that moves because its driven by the machine.
But what about the machine itself? It can go from A to B, but also from B to A without the need of energy since it is reversible. In principle, if reversible machines existed one should be able to design one that moves perpetually like A-->B-->A-->B-->A...

What am I missing?

Regards
Sure, but that isn’t what defines a perpetual motion *machine*. A perpetual motion machine needs to do work, not just move.
 
  • #3
+1

Otherwise the motion of planets would count as pm.
 
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Likes sophiecentaur

Related to Feynman: Reversible machines, no perpetual motion?

1. What are Feynman's reversible machines?

Feynman's reversible machines are theoretical machines that can operate in both forward and reverse directions, without any energy loss. They follow the laws of thermodynamics and do not violate the principle of conservation of energy.

2. Can Feynman's reversible machines achieve perpetual motion?

No, Feynman's reversible machines cannot achieve perpetual motion. They still require an energy input to function and do not provide a continuous output of energy without any input.

3. How do Feynman's reversible machines work?

Feynman's reversible machines work by using reversible processes, which are processes that can be reversed by a small change in the system. This allows them to operate in both forward and reverse directions without any energy loss.

4. What is the significance of Feynman's reversible machines?

Feynman's reversible machines have significance in the field of thermodynamics and the study of energy. They provide a theoretical model for machines that can operate with high efficiency and minimal energy loss.

5. Are there any real-life applications of Feynman's reversible machines?

Currently, there are no practical applications of Feynman's reversible machines. However, the concept has been used in the development of reversible logic gates in computer science and in the design of highly efficient heat engines.

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