What is perpetual motion?

[Achilles]

I think I heard Richard Feynman say that electrons move around the nucleus in perpetual motion. What does he mean by this? Sorry if I am wrong, if I am, please explain perpetual motion. 

[studiot]

1 hour ago, Achilles said:

I think I heard Richard Feynman say that electrons move around the nucleus in perpetual motion. What does he mean by this? Sorry if I am wrong, if I am, please explain perpetual motion. 

+1 for a pearl in all the trash being offered here at the moment.

There is a difference between 'perpetual motion' and 'a perpetual motion machine.'

The latter is declared impossible by the second law of Thermodynamics, even in theory with 'perfect or ideal' components (eg no friction).

Perpetual motion itself is required by two laws of Physics.

Newton's First Law

Earnshaw's theorem.

 

The difference is that a machine produces some sort of effect (usually mechanical work) in its environment.

A Newtons Firstly law particle does not interact with its environment, but travels on forever.

As to Feynman's comment;

If we regard an electron as a (charged) particle then it is subject to Earnshaw's theorem that states it is impossible for two or more charged particles to remain in static equilibrium, without external restraint.

So if there is more than one charged particle in a system they  must be in perpetual motion.

 

[Function]

34 minutes ago, studiot said:

As to Feynman's comment;

If we regard an electron as a (charged) particle then it is subject to Earnshaw's theorem that states it is impossible for two or more charged particles to remain in static equilibrium, without external restraint.

So if there is more than one charged particle in a system they  must be in perpetual motion.

Greetings! Do electrons and protons lose energy over time, as would a magnet lose its "magnetic strength/power" over (long) time?

If not, then isn't their perpetual motion at variance with the laws regarding conservation of energy?

[studiot]

1 hour ago, Function said:

Greetings! Do electrons and protons lose energy over time, as would a magnet lose its "magnetic strength/power" over (long) time?

If not, then isn't their perpetual motion at variance with the laws regarding conservation of energy?

Electrons in general do not 'decay' . They can be consumed or generated entirely in some exotic particle physics reactions.

Electrons are fundamental particles.

Protons have an internal structure and  have a very long half life, exceeding that of the known age of the universe by many orders of magnitude.

Proton generation is more common since neutrons are unstable ouside the nucleus and decay into protons.

 

How can their motion be at variance with energy conservation?

If they don't change their motion no energy (change) is involved.

If they do change their motion, the usual laws apply.

 

[swansont]

1 hour ago, Function said:

Greetings! Do electrons and protons lose energy over time, as would a magnet lose its "magnetic strength/power" over (long) time?

If not, then isn't their perpetual motion at variance with the laws regarding conservation of energy?

Charges undergoing acceleration will radiate, so a classical system with accelerating charges (any non-straight-line motion) will lose energy over time. But in QM there is no classical motion, and thus no acceleration. In addition, there is no way to lose energy if you're in the ground state.