Would this work? (zero-gravity perpetual generator)

[reitz]

I know that electricity can be produced by moving a wire through a magnetic field. It seems to me that the reverse should also work; keep the wire stationary and move the magnetic field. From that, I would assume that a generator could be constructed with coils of wire surrounding a spinning magnet (or maybe a cylinder with many magents affixed to the surface).

From physics, I know that an object in motion will remain in motion until acted upon by an outside force. From that, I would assume that if I were to place a cylinder into a zero-gravity vacuum and rotate it, it should spin indefinitely.

Would it be possible to construct a generator to take advantage of this? Coils of wire would surround a tube containing a free-floating, spinning magnetic cylinder. It would take energy to put the cylinder into motion, but without friction or gravity to slow it down or stop it, shouldn't it generate electricity indefinitely?

It's been five years since I've had a physics class, so I think I'm missing something simple. Would this idea work? If not, what am I missing?

 

[Stealth1024]

No it is not.

There are forces here that are not being taken into consideration, such that there will be a reaction to the force exerted onto the electrons by the magnet.

 

[stebesplace]

On a large scale, something large enough to power, say, a resiedntial block for lights; This application would be of no use. If it were even possible, you would need a large enough object to spin, which could cause enough electricity, hence how would you start to spin it? How do you stop it? Lots of mechanical problems i could think of.

Col Fusion man

-Steve

 

[f95toli]

This would not work for one simple reason: The electrical current generated in the spinning cylinder would create an opposite (and equal) counter-force that would make the cylinder stop spinning, this is the so-called Lentz law (I am not sure I remember the name of the guy).


You can not create energy, that is the most fundamental law there is in physics.

 

[FuriousBroccoli]

Originally posted by: f95toli
You can not create energy, that is the most fundamental law there is in physics.

Who's to say he's *creating* energy? I'm not arguing that this works, of course.

 

[Stealth1024]

same thing I said <FONT size=1>f95toli </FONT>

 

[stebesplace]

can not create energy?

correct me if i'm wrong, but when you rub your hands together, does that not create energy? What about a hydro damn, water, creating motion creating energy. I am not a smart man, but i am fairly sure that when i see a hand crank toy that spins fast enough to create an electric spark, that-that in itself is energy there. . .ohh well. . .

go ahead and build it, see what happens.

-Steve

 

[f95toli]

Who's to say he's *creating* energy? I'm not arguing that this works, of course.

The question was "shouldn't it generate electricity indefinitely?" and then the answer is no because you need energy to generate electricity (one could of course let the current flow in a superconduting loop but then you can not use the energy and you can not "add" more).

 

[f95toli]

Originally posted by: stebesplace
can not create energy? correct me if i'm wrong, but when you rub your hands together, does that not create energy? What about a hydro damn, water, creating motion creating energy. I am not a smart man, but i am fairly sure that when i see a hand crank toy that spins fast enough to create an electric spark, that-that in itself is energy there. . .ohh well. . . go ahead and build it, see what happens. -Steve

Rub your hands=Converting kinetic energy ("motion" energy) to heat
Hydro dam=Converting the potential energy of the water to electricity
Crank toy=Converting kinetic energy to electricity

 

[Bitek]

Right, you are not creating energy, but merely converting forms of E. In your example, you would be converting the movement, or kenetic E, into electrical E. As this happens, the spinning object would lose is KE, and eventually stop.

Look at your car's alternator. (sp?) It takes several hp to turn it at engine speeds. The engine must turn it, not to overcome gravity or friction, but that is the source of the energy which is given to electrons in order to produce electricity.

 

[KilroySmith]

Simple experiment:

Pick up a small dc motor - like out of a children's toy, or a slot car.

Spin the armature (the spinny thing). It'll spin for several seconds as it slows to a halt.

Now, short the two wires coming from the motor (or the two power terminals, if there are no wires). Try spinning the armature. It will come to a halt almost immediately.

Why?

Because when you spin the motor, you're generating electricity (if you put a voltmeter across the wires, you'll see Voltage). If the wires are not connected, no current can flow, no power is generated (power = voltage x current), so it spins until friction brings it to a halt.

If the wires are connected, a current flows, you generate power, which can only come from the kinetic energy of the spinning armature. There really isn't much of that, so it slows it down as effectively as if it were a brake.

/frank

 

[blahblah99]

Hafen is right, you cannot create or destroy energy - only convert from one form to another, whether its mass, light, potential, kinetic, or heat. Comon people, don't tell me you forgot Einstein and his E=mc^2 already

If you REALLY want to make money, do some research on how to turn a mass of water into energy

And for the zero-gravity perpetual generator, remember the high school physics law, for every action, there's an equal and opposite reaction. So if you get punched in the face, the nature of physics will predict that you will punch the person back in the face.

 

[PowerEngineer]

Reitz, your description of a rotating magnet producing changing manetic fields through stationary coils to induce current is a pretty accurate description of a standard synchronous generator that is the main-stay of electrical power generation today. What you are "missing" is that the interaction of the magnetic field from the rotating magnet and the magnetic field produced by the current in the stationary coils produces a torque on the rotating magnet that decelerates it. That's why these generators always need a "prime mover", by which we mean a source of energy to counteract this torque and keep the magnet spinning. The "prime mover" can be a steam turbine (where heat to produce the steam comes from fossil or nuclear fuel, or geothermal), a hydro turbine (turned by the falling water), or a wind turbine. And as others have said, the amount of energy the "prime mover" provides must be equal to the amount of electrical energy being generated; otherwise the generator will accelerate of decelerate.

 

[lukatmyshu]

Anyone find it funny that we can not only create energy, but we can't create perpetual motion ... so even if somehow the cylinder 'could' still rotate it would still slow down eventually (due to interactios with particles in the atmosphere, etc.)

 

[Jeff7]

Originally posted by: lukatmyshu
Anyone find it funny that we can not only create energy, but we can't create perpetual motion ... so even if somehow the cylinder 'could' still rotate it would still slow down eventually (due to interactios with particles in the atmosphere, etc.)

As has been said, we can't create energy! It can only be converted among various forms.
As for perpetual motion, that would require the absolute elimination of friction in the device's environment.
Also, observing a perpetual motion device would be impossible - once you shine light on it to observe it, you've introduced energy into the envorinment, which cannot be done, otherwise, it's not truly a perpetual device.

 

[nirgis]

Originally posted by: lukatmyshu
Anyone find it funny that we can not only create energy, but we can't create perpetual motion ... so even if somehow the cylinder 'could' still rotate it would still slow down eventually (due to interactios with particles in the atmosphere, etc.)

You can create perpetual motion. Rotating object in zero gravity in a perfect vacuum. Just because we can't simulate these conditions doesnt mean anything

 

[Jeff7]

Originally posted by: nirgis

Originally posted by: lukatmyshu
Anyone find it funny that we can not only create energy, but we can't create perpetual motion ... so even if somehow the cylinder 'could' still rotate it would still slow down eventually (due to interactios with particles in the atmosphere, etc.)

You can create perpetual motion. Rotating object in zero gravity in a perfect vacuum. Just because we can't simulate these conditions doesnt mean anything

But of course, you still can't observe it. It introduces energy, and also, friction. Light hitting something does exert a force on it.

 

[Rainsford]

Originally posted by: f95toli
This would not work for one simple reason: The electrical current generated in the spinning cylinder would create an opposite (and equal) counter-force that would make the cylinder stop spinning, this is the so-called Lentz law (I am not sure I remember the name of the guy).


You can not create energy, that is the most fundamental law there is in physics.

Bingo. When you induce a current in a wire with a changing magnetic field, the induced current will itself also produce a magnetic field that will oppose the change in the magnetic field that created the current in the first place.

 

[Shalmanese]

Jeff, the impossibility of a perpetual motion machine does not come from the perpetual or the motion part, it comes from the machine. Its easy to have perpetual motion, electrons spinning around an atom is perpetual motion. The problem is that there is no way for us to harness that energy.

 

[pspada]

I designed one of these when I was 5. Only works well outside of any gravity well, tho.

 

[TSDible]

Originally posted by: f95toli

Originally posted by: stebesplace
can not create energy? correct me if i'm wrong, but when you rub your hands together, does that not create energy? What about a hydro damn, water, creating motion creating energy. I am not a smart man, but i am fairly sure that when i see a hand crank toy that spins fast enough to create an electric spark, that-that in itself is energy there. . .ohh well. . . go ahead and build it, see what happens. -Steve

Rub your hands=Converting kinetic energy ("motion" energy) to heat
Hydro dam=Converting the potential energy of the water to electricity
Crank toy=Converting kinetic energy to electricity

For the most part that is correct. Not to nit pick... ok ok... to nit pick...

The Hydro dam is also a Kinetic energy -> Electric Energy conversion. The "motion" of the water is what is converted into electric energy.

My physics teacher told me... oh wait... I am the physics teacher... nevermind.
(only an intro to physics though so don't start posting all of your outrageous questions to me...

These guys are correct though... the Law of Conservation of Energy states (basically) that Energy can not be created or destroyed by ordinary means. It can only be converted from one form to another...

 

[f95toli]

The potential energy of the water is converted into kinetik energy as it goes trough the turbine and the turbine converts the kinetic energy to electricity.
The potential energy of 1000 m^3 water 100 m over the surface of the dam is 1*1000*9.8*100=98 000 000 J which means that you can get 27 kWh of electricity from it assuming 100% conversion efficiency.

f95toli
-also a physics teacher (sometimes)

 

[TSDible]

Originally posted by: f95toli
The potential energy of the water is converted into kinetik energy as it goes trough the turbine and the turbine converts the kinetic energy to electricity.
The potential energy of 1000 m^3 water 100 m over the surface of the dam is 1*1000*9.8*100=98 000 000 J which means that you can get 27 kWh of electricity from it assuming 100% conversion efficiency.

The fact that you say "as it goes through" implies that the water is already in motion. Therefore, the energy that the water has is already kinetic... I think that you are confusing the energy that the water has with G.P.E. (gravitational potental energy), sometimes called the energy of position. As your equation for GPE implies... The conversion is more like...

kinetic -> kinetic -> electric

The first conversion isn't really a conversion at all, just a transfer.

If you wnat to include the the G.P.E. conversion as the water has to crest over a falls so to speak then there is even more... Then you would have...

G.P.E. -> kinetic (as the water starts to fall) -> kinetic (transfered to the turbines) -> electric

Not all dams involve the G.P.E. part though... some just open flood gates and use bernoulli's principle to make the water flow at a faster rate to turn a turbine. Actually, I think that is the case with most dams, but I could be wrong.

That was fun... I need to get back in the classroom.

 

[f95toli]

I was assuming that the water falls 100m before hitting the turbine (the water is initally at rest in the water magazine). I know 100 mis too much (20-30 m is probably more reasonable) but it was easy to calculate.
My calculation just showed the maximum amount of energy you can get from 1000 m^3 water, how many times the energy is converted between diffrent forms of energy before it becomes electricity is irrelevant as long as you have 100% conversion efficiency at each stage.

 

[TSDible]

True, true...

Your's does show the maximum energy that can be created by using "falling" water. But as I said, I believe that many dams use Bernoulli's Principle instead of gravity to generate the energy. So, they would actually use the formula for kinetic energy...

K.E. = 1/2 m*v^2

So, in theory, it could produce more energy that way as you could get the water to move more quickly based on the depth and size of the flood gates on the damn. The energy is actually exponential based on the speed that you can get the water to travel.

Of course, Your's uses the same thing, and if you set your G.P.E. = K.E., the masses would cancel out, and you could calculate the theoretical maximum speed of a falling object. In this case water. You are limited by that velocity, which of course is based only on how far the water falls.

Or something like that...

to be honest, I'm not even sure if my way could produce more energy as I don't have the needed equations handy for Bernoulli and Pressure based on depth of water handy. But I don't think it is as limited as the falling water.