Creating a Generator in Orbit: Where Am I Going Wrong?

[jaydnul]

I had a thought. Without friction, the conductor in between the magnet would spin indefinitely in orbit (free of gravity). Tell me where I am going wrong

 

[Whovian]

Well, first of all, the generator would slow down anyways, because it outputs energy and thus must lose energy.

Second, space, contrary to popular belief, is not truly devoid of matter, its "atmosphere" is just very, very, very, very, very, very, very, very, very, very, very thin. The Second Law tells us that we can't have a truly frictionless system, too.

 

[Alfang]

Are you trying to say that the rotor in a generator will spin freely or with less drag?
You still need force to induce current into those coils, it's still going to be like pushing two positive poles of two strong magnets together.
Your going to still have to put in a bit more energy than you get out.

 

[jaydnul]

Oh i see, so the actual current that is induced will remove energy from the motion?

 

[Drakkith]

Oh i see, so the actual current that is induced will remove energy from the motion?

Yes. It takes work to cause current to flow, and this work is done by turning the magnet. If you stop applying a force to turn the magnet it will quickly stop.

 

[HallsofIvy]

I have been asked this question a number of times, usually by high school students. They seem to be under the impression that there would be no friction "in orbit" which just isn't true.

Obviously, any output will reduce the energy but even without that there will be resistance and so eventually, the mechanism will stop. There will, for one thing, be resistance in the wires. That has nothing to do with being in space. There will be no air resistance but there would still be friction at any rotating piece. And, while there will be no gravitational force, in order to have the mechanism work, instead of just falling apart, you will have some force holding the pieces together. And that will cause friction losses.

 

[CWatters]

Oh i see, so the actual current that is induced will remove energy from the motion?

Yes. See also http://en.wikipedia.org/wiki/Lenz's_law

Lenz's law states that the current induced in a circuit due to a change in the magnetic field is so directed as to oppose the change in flux or to exert a mechanical force opposing the motion.

That's why it takes mechanical energy to spin a generator or dynamo that is connected to a load. It's not just a case of friction or air resistance that can be eliminated by putting the generator in space.

You can also think of it as a consequence of the law of conservation of energy.

 

[jaydnul]

What if we found a way to harness the Earth magnetic field to create a source of energy? Would the eventually stop the rotation of the Earth's core? Would that be bad, other than not having any working compasses anymore?

 

[dbmorpher]

What if we found a way to harness the Earth magnetic field to create a source of energy? Would the eventually stop the rotation of the Earth's core? Would that be bad, other than not having any working compasses anymore?

That would be bad, very bad. You see the Earth's core's magnetic rotations produce the Van Allen Belts. These Belts protect the Earth's atmosphere from particles moving close to the speed of light from the sun.

But to turn the Earth into a generator we would need to crash Venus and Mars into it. Generators get energy from resistance, any magnets that would have enough power to get resistance from the Earth's core would have to be a lot bigger than what we can make now, trust me I live near the world's largest.

 

[sophiecentaur]

"Harnessing" the Field would mean changing it (reducing it). There is a massive difference between a Field and Energy and it is usually this confusion that produces the perennial questions about endless sources of energy.