> (1) the physically impossible perpetual motion of popular understanding, e.g. machine that operates at 100% energy efficiency in perpetuity from an initial one-time energy input

That's easy to make. If you spin up a wheel in the vacuum of space, it's going to keep spinning forever.

If doing it in space is not allowed, then you have to allow machines that take advantage of terrestrial conditions such as drawing energy from ambient sources.

▲

glenstein 3 days ago | parent | next [-]

>If doing it in space is not allowed, then you have to allow machines that take advantage of terrestrial conditions such as drawing energy from ambient sources.

Well yeah, that's (2), not (1), so no one's disallowing those.

Edit: And although it's kind of moot, I'm not sure what the relationship is between space and ambient draw such that disallowing one would necessitate allowing the other.

▲

carlosjobim 3 days ago | parent [-]

If you're not allowing the machines to be tested in space (no environmental factors) nor on earth (environmental factors), then there's nowhere allowed to test or make such a machine. So a perpetual motion machine becomes impossible because there is nowhere in the universe where they are accepted.

Is it possible for a man to run 100m in less than 10 seconds? If he's not allowed to run on any kind of surface. So now we've proven that it's impossible to run 100m in less than 10 seconds?

	▲	lo_zamoyski 2 days ago \| parent \| next [-]
		There's a difference between impossible in principle and impossible in practice. Science is interested in principle. Engineering is interested in practice. You don't need to walk 1000km or 1001km or 1002 km to know that, in principle, these can be done.
	▲	glenstein 3 days ago \| parent \| prev [-]
		The first and second laws of thermodynamics would apply regardless of where you stage the experiment.

▲

hermitcrab 4 days ago | parent | prev [-]

>If you spin up a wheel in the vacuum of space, it's going to keep spinning forever.

Even interstellar space is not 100% vaccuum. So it will slow from the occasional contact with matter. No doubt it would take a very long time, though.

	▲	glenstein 2 days ago \| parent [-]
		Right. And also efficiency is about its interaction as part of a system, which is the difference between perpetual motion, and perpetual motion machine.