The discussion centers on the concept of perpetual motion as referenced in Richard Feynman's "Lectures Vol I," specifically in chapter 4-2 regarding gravitational potential energy. Feynman posits that while perpetual motion can be theoretically defined in the context of weight-lifting machines, it ultimately contradicts the law of conservation of energy. The forum participants clarify that perpetual motion, as commonly understood, is impossible and that discussions on this topic are banned due to their tendency to attract pseudoscientific claims.
PREREQUISITESStudents of physics, educators, and anyone interested in the principles of energy conservation and the scientific method will benefit from this discussion.
Vanadium 50 said:He most certainly does not mean we can have "perpetual motion" in the usual sense of the word (which is a banned topic here) - a machine that continually produces energy.
What's the exact reference?iVenky said:I was reading Feynman's lectures Vol I. There he says it is possible to have perpetual motion ideally.
Consider weight-lifting machines—machines which have the property that
they lift one weight by lowering another. Let us also make a hypothesis: that
there is no such thing as perpetual motion with these weight-lifting machines.
(In fact, that there is no perpetual motion at all is a general statement of the law
of conservation of energy.) We must be careful to define perpetual motion.
First, let us do it for weight-lifting machines. If, when we have lifted and lowered
a lot of weights and restored the machine to the original condition, we find that
the net result is to have lifted a weight, then we have a perpetual motion machine
because we can use that lifted weight to run something else. That is, provided the
machine which lifted the weight is brought back to its exact original condition,
and furthermore that it is completely self-contained—that it has not received the
energy to lift that weight from some external source
It is a very beautiful line of reasoning. The only problem is that perhaps it is not
true. (After all, nature does not have to go along with our reasoning.) ,For example,
perhaps perpetual motion is, in fact, possible. Some of the assumptions may be
wrong, or we may have made a mistake in reasoning, so it is always necessary to
check. It turns out experimentally, in fact, to be true.
iVenky said:Just for curiosity why is this topic (perpetual motion) banned?
Thanks