Isn't gravitational orbit perpetual motion?

[Haroldingo]

I was wondering... Suppose that the mass that was being orbited, in place of the earth, was stable and constant - then substitute the moon with another constant but suppose the orbit is the same as the mass and distances between them are the same - would/could this be an example of perpetual motion?

 

[Drakkith]

This doesn't make any sense. What does "substitute the moon with another constant" mean? Why do you even need to replace the Earth and the moon in this scenario?

In any case, an orbiting body, ignoring any slight deceleration from impacts with atoms and subatomic particles in space, is "perpetual motion". There is nothing against that. The issue is with perpetual motion "machines". And even more so with machines designed to generat an outpute greater than their input while using no fuel. Stay away from either of those and you will be fine.

 

[Haroldingo]

@ Drakkith , sorry, my wording was poor. I mean to say that over time the moon and the Earth will deteriorate and therefore the orbit will change and eventually cease to exist. So by a constant I just mean something with the exact same properties apart from deterioration.

Ok I getcha. But would it not be possible to reproduce gravitational orbit on a smaller scale ?

If we ever manage to understand how gravity really works then it should be possible.. maybe even know with enough experimentation. The key to perpetual motion should be gravity, because if it's an accepted possibility as you said, then the fuel output of a replica should be next to 0? Considering that the Earth doesn't run on fuel, nor the moon..

 

[rcgldr]

"Perpetual motion" is somewhat of a misnomer applied to devices that can supposedly output more energy than input. It's also unusual for any real process to be completely free of any losses, since for example space isn't a perfect vacuum, so there is some drag on any object moving in space. A current flowing through a true superconductor would be perpetual motion, and such a device could be useful for storing energy, but not for producing energy.

 

[Drakkith]

The Earth and the moon formed from the collapse of a nebula. This collapse of this mass of gas and dust and such gave it rotational speed that resulted in the current velocities of the planets. The formation of the moon was similar, except that it is theorized that a large object struck the earth, ejecting the material that formed the moon. This is where the initial energy came from for the planets and moons to stay in their orbit. It is not infinite and does not require a continual expediture of energy.

The key to perpetual motion should be gravity, because if it's an accepted possibility as you said, then the fuel output of a replica should be next to 0?

The key to perpetual motion is the elimination of all resistance to said motion. There isn't any real benefit other than storing energy in something like maybe a flywheel or something.

 

[Pengwuino]

Gravitational orbits are probably not even perpetual motion machines in the sense that Drakkith is mentioning. Orbiting bodies probably give off gravitational radiation which would cause the orbits of the planets to eventually cease and cause a collision.

 

[treehouse]

A stable atom is a perpetual motion machine - its electron(s) perpetually orbit its nucleus.

 

[Pengwuino]

A stable atom is a perpetual motion machine - its electron(s) perpetually orbit its nucleus.

Although quantum mechanically, orbits don't even make sense to talk about.

 

[Drakkith]

A stable atom is a perpetual motion machine - its electron(s) perpetually orbit its nucleus.

An atom is not a machine, nor are electrons similar to little planets in orbit. The wave function of the electron is more like a standing wave I believe. (Or so my illustrated guide to quantum physics book tells me. It's got pictures!)

 

[treehouse]

Whatever: the electron(s) in a stable atom will perpetually keep moving the way they move or those waves we represent as electrons will perpetually do what they do in a stable atom.

 

[Pengwuino]

Whatever: the electron(s) in a stable atom will perpetually keep moving the way they move or those waves we represent as electrons will perpetually do what they do in a stable atom.

That's not how atoms work.

 

[treehouse]

How is that not how atoms work?

 

[pallidin]

Why do some think that the moon orbiting the Earth is somehow an example of "perpetual motion" ??
Eventually(a long, long time) the moon will impact our earth.

 

[Pengwuino]

How is that not how atoms work?

Protons and electrons are not these pointlike particles that orbit each other. If they were, the electron would radiate away and almost instantly fall into the proton. Bohr's theory/quantum mechanics addresses the fact that both particles are not point-like orbiting bodies like planets.

 

[Drakkith]

Whatever: the electron(s) in a stable atom will perpetually keep moving the way they move or those waves we represent as electrons will perpetually do what they do in a stable atom.

The issue here is where most people use the word machine.

Machine: A machine manages power to accomplish a task, examples include, a mechanical system, a computing system, an electronic system, a molecular machine and a biological machine. In common usage, the meaning is that of a device having parts that perform or assist in performing any type of work. A simple machine is a device that transforms the direction or magnitude of a force.

A stable atom simply sitting there is NOT a machine. You can make it into a machine, but to get work out of it you have to input energy. Perpetual motion by its very definition cannot apply to a machine and its output.

 

[Ryan_m_b]

Perpetual motion as in moving in perpetuity is not the same as what is meant by the term "perpetual motion machine".

The idea behind a PMM is that a circular system is constructed (i.e. it has components that interact with each other, the last interaction restarts the first). In real life such a machine would inevitably stop working because the initial energy is lost to friction, resistance, waste heat etc. So for such a circular system to work there must be absolutely zero energy loss. This in itself is not possible.

But in addition to this proponents of PMMs advocate that not only can they build a machine that has zero energy loss (i.e it can be in motion perpetually) they can extract energy from the machine to do work without losing energy. This is even more impossible.

To use the analogy of an orbiting system. Imagine we have one magnetic object orbiting a mass in a stable orbit. The orbit may last perpetually. Now imagine that we try to extract energy from such a system, perhaps by building a torus around the magnet's orbit, as the object moves through it it generates electricity. But in the process of extracting this energy we are creating resistance and slowing down the magnet. This will change it's orbit, ultimately making it fall.

 

[sicarius]

Why do some think that the moon orbiting the Earth is somehow an example of "perpetual motion" ??
Eventually(a long, long time) the moon will impact our earth.

Actually the moon is moving away from the Earth and will eventually break free (unless we are swallowed up by the sun becoming a red giant first).

 

[Haroldingo]

Am I incorrect in the assumption that electrons don't actually orbit the nucleus?

Electro-statical energy keeps the electrons within a perfect distance of the nucleus, Schrödinger's wave function principle (Kinetic energy + Potential Energy = E), the electron is both a wave and a particle at the same time, and as it exists in more than one physical state simultaneously it isn't actually orbiting, and even in the aspect that it is orbital, gravity isn't the force that causes it to be so.

 

[maverick_starstrider]

Am I incorrect in the assumption that electrons don't actually orbit the nucleus?

Electro-statical energy keeps the electrons within a perfect distance of the nucleus, Schrödinger's wave function principle (Kinetic energy + Potential Energy = E), the electron is both a wave and a particle at the same time, and as it exists in more than one physical state simultaneously it isn't actually orbiting, and even in the aspect that it is orbital, gravity isn't the force that causes it to be so.

The word orbit does not apply exclusively to gravity, a positively charged ball could orbit a negatively charged ball. That being said saying electrons "orbit" can rub physicists the wrong way since the math (and thus the physical reality) of quantum mechanics is nothing like that (for example, the position eigenvalue of an electron has no time dependence which is completely unlike some dot orbiting a bigger dot, and yet the have an angular momentum). Though for historical reasons we do still say electrons are restricted to ORBITALS.

However, in response to your main question, you're parsing the words "perpetual" "motion" "machine" but you don't seem to actually understand what the phrase as a whole means. Perpetual motion exists, that's not even close to the issue, any system in some sort of stable equilibrium could probably be said to be in some form of perpetual motion. The issue is crackpots who claim they have invented a perpetual motion MACHINE. What this means is they claim they've found some cycle (usually involving magnetism, because magnetism is mysterious to a lot of layman) in which usable work can be taken out of the system without in any way diminishing the energy of the system. Perhaps we should call them "Machines undergoing perpetual, undiminishing, motion despite constantly giving away energy to their environment". But that's kind of a mouthful.

 

[Pengwuino]

Am I incorrect in the assumption that electrons don't actually orbit the nucleus?

No, you are right.

 

[Haroldingo]

The word orbit does not apply exclusively to gravity, a positively charged ball could orbit a negatively charged ball. That being said saying electrons "orbit" can rub physicists the wrong way since the math (and thus the physical reality) of quantum mechanics is nothing like that (for example, the position eigenvalue of an electron has no time dependence which is completely unlike some dot orbiting a bigger dot, and yet the have an angular momentum). Though for historical reasons we do still say electrons are restricted to ORBITALS.

However, in response to your main question, you're parsing the words "perpetual" "motion" "machine" but you don't seem to actually understand what the phrase as a whole means. Perpetual motion exists, that's not even close to the issue, any system in some sort of stable equilibrium could probably be said to be in some form of perpetual motion. The issue is crackpots who claim they have invented a perpetual motion MACHINE. What this means is they claim they've found some cycle (usually involving magnetism, because magnetism is mysterious to a lot of layman) in which usable work can be taken out of the system without in any way diminishing the energy of the system. Perhaps we should call them "Machines undergoing perpetual, undiminishing, motion despite constantly giving away energy to their environment". But that's kind of a mouthful.

Ok, I get it :) So Perpetual motion occurs in nature, but cannot (as we know so far), be replicated mechanically?

No, you are right.

Yay! I got something right :')

 

[Drakkith]

Ok, I get it :) So Perpetual motion occurs in nature, but cannot (as we know so far), be replicated mechanically?

I guess it depends on what you count as perpetual motion. Orbits of planets and stars are not perpetual, but an electron in it's orbital is unless disturbed, but its up in the air whether you could consider that perpetual motion.

 

[russ_watters]

Ok, I get it :) So Perpetual motion occurs in nature, but cannot (as we know so far), be replicated mechanically?

Well, no, not really. "Perpetual motion" just isn't a term used by scientists so it's tough to say what exactly it means. If taken as literally as possible, it just means "moving forever", which sounds a lot like Newton's First Law:

I. Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

http://csep10.phys.utk.edu/astr161/lect/history/Newton3laws.html

So there's nothing all that special about that definition.

But when used by budding crackpots, it typically refers to a machine that can operate forever and generate energy. That's what's impossible. Please read the wiki on that subject:

Perpetual motion describes hypothetical machines that operate or produce useful work indefinitely and, more generally, hypothetical machines that produce more work or energy than they consume, whether they might operate indefinitely or not...

One classification of perpetual motion machines refers to the particular law of thermodynamics the machines purport to violate:[2]

-A perpetual motion machine of the first kind produces work without the input of energy. It thus violates the first law of thermodynamics: the law of conservation of energy.

-A perpetual motion machine of the second kind is a machine which spontaneously converts thermal energy into mechanical work. When the thermal energy is equivalent to the work done, this does not violate the law of conservation of energy. However it does violate the more subtle second law of thermodynamics (see also entropy). The signature of a perpetual motion machine of the second kind is that there is only one heat reservoir involved, which is being spontaneously cooled without involving a transfer of heat to a cooler reservoir. This conversion of heat into useful work, without any side effect, is impossible, according to the second law of thermodynamics.

A more obscure category is a perpetual motion machine of the third kind, usually (but not always)[3] defined as one that completely eliminates friction and other dissipative forces, to maintain motion forever (due to its mass inertia). Third in this case refers solely to the position in the above classification scheme, not the third law of thermodynamics. Although it is impossible to make such a machine,[4][5] as dissipation can never be 100% eliminated in a mechanical system, it is nevertheless possible to get very close to this ideal (see examples in the Low Friction section). Such a machine would not serve as a source of energy but would have utility as a perpetual energy storage device.

http://en.wikipedia.org/wiki/Perpetual_motion