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Author Topic: Can anyone tell me why this won`t work  (Read 3390 times)

Offline rayhelm

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Can anyone tell me why this won`t work
« on: 18/11/2007 19:46:36 »
Looking at some old footage of a satellite being launched from the space shuttle, I was struck by the spin imparted by the launch cradle when the satellite was released I thought that it would spin like that until the orbit decayed and it was destroyed.
This got me thinking about terrestrial power generation. If you could support a generator spindle on magnetic bearings and pump out the casing to reduce friction, would this not also spin indefinitely once an initial impetus was applied.
Clearly I am missing something fundamental here, otherwise we would be generating all our power this way already!


 

another_someone

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Can anyone tell me why this won`t work
« Reply #1 on: 18/11/2007 20:11:10 »
Certainly, gyroscopes have been built where the rotor is spinning in a vacuum and on magnetic bearings, and although there is some slight loss of energy, it is very very slight.

The problem with electrical generators is that once you take energy out if the system, then clearly the energy has to come from somewhere.

An electrical generator works by moving a conductor through a magnetic field.  The magnetic field induces a current flow in the conductor (which is where you get your electrical energy), but the current flow itself creates its own magnetic field, and the magnetic field in the current opposes the magnetic field in which it is moving through, thus forcing the conductor to slow down,

Thus you conserve the energy in the system, as you allow the current to flow through the conductor, it is generating a magnetic field then opposes the motion of the conductor in the magnetic field, until the conductor ceases to move, and you have no more current.
 

lyner

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Can anyone tell me why this won`t work
« Reply #2 on: 18/11/2007 21:57:35 »
General principle: if you think you've invented perpetual motion, you haven't, I'm afraid. Energy has to come from somewhere.
 

Offline techmind

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Can anyone tell me why this won`t work
« Reply #3 on: 18/11/2007 23:57:39 »
The problem with electrical generators is that once you take energy out if the system, then clearly the energy has to come from somewhere.

An electrical generator works by moving a conductor through a magnetic field.  The magnetic field induces a current flow in the conductor (which is where you get your electrical energy), but the current flow itself creates its own magnetic field, and the magnetic field in the current opposes the magnetic field in which it is moving through, thus forcing the conductor to slow down,

If you have a small high-quality DC electric motor, such as the (high-speed) LEGO motor, you can demonstrate this effect.
1) with no electrical connection to the motor you can turn the spindle between your fingers - it'll be "lumpy" due to the magnet arrangement, but feel how much effort it takes. Now use some wires to "short circuit" the electrical connection, and try turning the spindle again. Notice it's harder, especially if you try and turn it quickly.
2) put a small flywheel on the motor spindle (such as a "wheel" from a large lego car). Apply power to the motor briefly to spin it up (don't let it go too fast, or the Lego tyre might fly off the wheel due to "centrifugal" forces!), then disconnect the power. It will gradually slow down due to friction etc. Now short-circuit the motor terminals (or connect several lightbulbs in parallel across it) - you'll see it slow down much more abruptly.
« Last Edit: 19/11/2007 00:00:02 by techmind »
 

Offline rayhelm

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Can anyone tell me why this won`t work
« Reply #4 on: 19/11/2007 18:24:22 »
Ok, thanks for the replies, there goes my chance to make a million!
 

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Can anyone tell me why this won`t work
« Reply #4 on: 19/11/2007 18:24:22 »

 

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