# How would this NOT work as a perpetual work/motion machine?

• CYP450
In summary, the proposed system of using two spherical magnets orbiting a common center of mass to generate electrical energy through a hollow torus with coiled wires is not a perpetual work/motion machine as it would eventually lose energy due to electromagnetic radiation and the opposing force of eddy currents. Lenz's Law also states that the generated current would oppose the motion of the spheres, causing them to slow down over time.
CYP450
So perpetual work/motion machines are impossible, but I've toyed with this idea for a hypothetical, super massive, planetary-scale electrical energy generator for a while.

Suppose you had 2 very large moon/planet-sized spherical magnets that were far enough so as to not attract magnetically but close enough to attract gravitationally. You then set these magnetic spheres in motion so that they start orbiting a common center of mass.

You then enclose the shared orbit in a hollow, stationary torus. You then coil the torus with wires. My idea is that as the magnetic spheres orbit around their common center of mass, they move along the inside of the hollow torus coiled with cables and generate an electrical current in it forever.

And yet it couldn't work forever. I just want to know how or why this system couldn't go on indefinitely.

CYP450 said:
So perpetual work/motion machines are impossible, but I've toyed with this idea for a hypothetical, super massive, planetary-scale electrical energy generator for a while.

Suppose you had 2 very large moon/planet-sized spherical magnets that were far enough so as to not attract magnetically but close enough to attract gravitationally. You then set these magnetic spheres in motion so that they start orbiting a common center of mass.

You then enclose the shared orbit in a hollow, stationary torus. You then coil the torus with wires. My idea is that as the magnetic spheres orbit around their common center of mass, they move along the inside of the hollow torus coiled with cables and generate an electrical current in it forever.

And yet it couldn't work forever. I just want to know how or why this system couldn't go on indefinitely.

The energy would be lost due to electromagnetic radiation. Oscillating magnets in any configuration would produce EM waves which carry energy away from the system.

Also, the magnets would produce eddy currents in the wires (that is the principle way it extracts power), but these currents produce an opposing field to these magnets slowing them down, transferring momentum from the magnets to the torus.

That being said, it would take a heck of a long time to rob an Earth sized magnet of its rotational kinetic energy in this way.

If you want to know what the actual source of the force that will slow down rotation of your moons/planets is, it's the coil. When a magnet moves and induces current in a coil, the induced current generates its own magnetic field. That magnetic field will always be oriented in a way as to slow down the moving magnet. This is why it takes certain amount of torque to turn generator, and why it allows to convert mechanical work into electricity.

How could you ever distance them so that they are affected by gravity and not the magnetic field?

Gibby_Canes said:
How could you ever distance them so that they are affected by gravity and not the magnetic field?

By "making" the intrinsic magnetic field of the planets very weak. Then the results of the magnetic force between the planets wouldn't be seen for long time scales. Of course, after a very long time it would perturb the orbits, and I'm not sure if the OP recognized that or not.

Steely Dan said:
By "making" the intrinsic magnetic field of the planets very weak. Then the results of the magnetic force between the planets wouldn't be seen for long time scales. Of course, after a very long time it would perturb the orbits, and I'm not sure if the OP recognized that or not.

ah. I am only just now starting to study E&M (excluding basic freshman E&M), so I wasn't sure if it would be possible considering how weak gravity is.

Gibby_Canes said:
How could you ever distance them so that they are affected by gravity and not the magnetic field?

If I'm not mistaken, doesn't the strength of a magnetic field fall off with the inverse cube of the distance instead of the inverse square like gravity does?

Drakkith said:
If I'm not mistaken, doesn't the strength of a magnetic field fall off with the inverse cube of the distance instead of the inverse square like gravity does?
For a dipole field, this is right, and therefore a larger distance does help to make gravity stronger than the electromagnetic force (from the dipoles). Higher orders would be possible and would fall off even quicker. However, you could just use two magnets with a rope in between and rotate that (or use rails and a single magnet), no need to get some fancy planet-sized magnets.

Anyway, the method of power extraction itself would slow down the movement.

mfb said:
Anyway, the method of power extraction itself would slow down the movement.
Exactly. Each joule of electrical or thermal energy extracted would reduce the orbital KE of the planet by 1 joule.

CYP450 said:
So perpetual work/motion machines are impossible, but I've toyed with this idea for a hypothetical, super massive, planetary-scale electrical energy generator for a while.

Suppose you had 2 very large moon/planet-sized spherical magnets that were far enough so as to not attract magnetically but close enough to attract gravitationally. You then set these magnetic spheres in motion so that they start orbiting a common center of mass.

You then enclose the shared orbit in a hollow, stationary torus. You then coil the torus with wires. My idea is that as the magnetic spheres orbit around their common center of mass, they move along the inside of the hollow torus coiled with cables and generate an electrical current in it forever.

And yet it couldn't work forever. I just want to know how or why this system couldn't go on indefinitely.

If I understood you correctly, you use the spheres' magnetic field to sweep the turns at different parts of the torus, and generate varying electromotive force.

But, if you remember Lenz's Law, the current that flows through the coils (you must draw current to get positive work from the system, an open circuit does not generate power) opposes the cause of its generation, in this case, the relative motion of the spheres with respect to the torus. Thus, the induced current generates a magnetic field that tries to slow down the spheres.

As they slow down, the gravitational foce forces them to go on an orbit with a smaller radius (remember that the centripetal acceleration is caused by the gravitational attraction of the spheres, so in equilibrium $v^2/r = G M/(2 r)^2 \Rightarrow r = G M/(4 v^2)$, the radius of the orbit is inversely proportional to the square of the orbital speed). Thus, the spheres start spiraling towards each other. They either hit the walls of the torus, or hit the planet around which they are orbiting.

Its not a bad idea, but its not perpetual energy. Basically you're talking about making a massive alternator that uses gravity to give you your mechanical motion and converting it into usable energy.

It looks like it will last forever, but it won't. The laws of thermodynamics still apply and eventually gravity will implode the system, and for that reason it can not be called perpetual energy. However, due to the massive scale you are talking about, once set up, it could last millions of years, just not forever.

The best perptual motion machine I have ever seen is this: Start with a vertical wheel on an axle. At the point on the wheel directly to the right of the center attach a 9 kg mass clearly labeled "9". Rotate the wheel, say, 60 degrees clockwise and add another such mass. Continue this around the wheel.

As the wheel turns the masses will turn over as they go past the bottom point and be labeled "6" instead of "9"! Since the masses on the right side are always larger than the masses on the left, the wheel will continue to turn!

HallsofIvy said:
The best perptual motion machine I have ever seen is this: Start with a vertical wheel on an axle. At the point on the wheel directly to the right of the center attach a 9 kg mass clearly labeled "9". Rotate the wheel, say, 60 degrees clockwise and add another such mass. Continue this around the wheel.

As the wheel turns the masses will turn over as they go past the bottom point and be labeled "6" instead of "9"! Since the masses on the right side are always larger than the masses on the left, the wheel will continue to turn!

## 1. How does the law of conservation of energy prevent a perpetual motion machine from working?

The law of conservation of energy states that energy cannot be created or destroyed, only transferred or converted. In order for a perpetual motion machine to work, it would need to continuously produce energy without any external input. This goes against the fundamental principle of energy conservation and is therefore not possible.

## 2. Can friction be eliminated to make a perpetual motion machine possible?

No, friction cannot be completely eliminated. Even in the most ideal conditions, there will always be some level of friction present. Friction causes energy to be lost in the form of heat, making it impossible for a machine to continue moving indefinitely without any additional energy input.

## 3. What about magnets and gravity? Can they be used to create a perpetual motion machine?

Magnets and gravity are both examples of conservative forces, meaning they do not dissipate energy. However, they still follow the law of conservation of energy. While they can be used to generate motion, they cannot create energy on their own, and therefore cannot sustain perpetual motion.

## 4. Is it possible to design a perpetual motion machine using multiple energy sources?

No, combining different energy sources does not change the fact that energy cannot be created or destroyed. In order for a machine to continuously move without any external input, it would need to create its own energy, which is not possible according to the laws of physics.

## 5. Are there any examples of perpetual motion machines that have been successfully created?

No, there are no verifiable examples of perpetual motion machines that have been created. Many people have attempted to design and build such machines, but they have all ultimately failed due to the laws of physics. Any claims of a perpetual motion machine working are likely a result of human error or a misunderstanding of the laws of physics.

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