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What is the difference between free energy (over unity) and perpetual motion?

Please provide some examples, both real world and theoretical.

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closed as not a real question by Deepak Vaid, Greg Graviton, nibot, David Zaslavsky♦ Feb 23 '11 at 17:19

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, see the FAQ.

1 Answer

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"Free energy" is a term used either by science or pseudoscience, and it means totally different things.

In pseudoscience, "free energy" is energy for free that can be created out of nothing and it is the same thing as a (source of) perpetual motion, and it's an impossible concept. Conspiracy theories exist that civilizations are suppressing evidence that energy may be created for free.

In actual science, free energy is the energy with an extra term, meaning the total energy that may be converted to work. Free energy is $$A=U-TS$$ which is the Helmholtz version or $$G=E+pV-TS$$ which is the Gibbs version. None of those energies is for "free" in the layman's sense - they're just different ways of counting energy and its transfer (including work) in which energy is ultimately conserved.

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I'll take it that you didn't understand the question. I asked what the difference is between overunity and perpetual motion. – Alex C Feb 23 '11 at 9:17
"Overunity" is not known to science. Do You believe in that energy for free nonsense? If so say it. I just googled for overunity, in fact this is a typical expression of energy for free . – Georg Feb 23 '11 at 12:22
sci·ence    –noun 1. a branch of knowledge or study dealing with a body of facts or truths systematically arranged and showing the operation of general laws: the mathematical sciences. 2. systematic knowledge of the physical or material world gained through observation and experimentation. 3. any of the branches of natural or physical science. 4. systematized knowledge in general. 5. knowledge, as of facts or principles; knowledge gained by systematic study. 6. a particular branch of knowledge. 7. skill, especially reflecting a precise application of facts or principles; proficiency. – Alex C Feb 23 '11 at 13:32
Alex, I'll take it that you don't understand basic physics and are not interested in real answers – user346 Feb 23 '11 at 14:06

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