pucture a pinwheel. now have a motor spin it. in space, the handle will rotate around the wheel (equal force on both the spinner and spinee). now imagine the handle has another pinwheel on the other end of it, and it spins, too, switching between accelerating it and the other wheel if neccacary. would it not be possible, in this fashion to move a vehicle forward in space?
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Anonymous2006-06-13 14:13
Nope. Newton's third law, or Conservation of momentum.
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Anonymous2006-06-13 14:47
ok, I looked it up, I remember the whole "momentum of an isolated system is constant" thing now, but WHY wouldn't it work? what would happen to it?
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Anonymous2006-06-13 15:21
It wouldn't rotate about the endpoints, but about the centre of mass. So the whole thing would just wiggle around in the same spot.
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Anonymous2006-06-13 15:54
>>4
If it was allowed to do that indefinitely, would it surpass the speed of light?
>>5
a rotating body can be considered to have a velocity in the direction of rotation at that instand at a speed equal to, well, the velocity of rotation. say that theroretically the object could handle the sheer forces involved here (it couldn't). the object in question would gain mass as it's velocity came very close to the speed of light and never quite reach it, just like any other object.
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Anonymous2006-06-13 17:27
>>6
What if I shoot a massive load on it with my male bazooka when it is really close? Surely no force in the Universe can withstand such a power!
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Anonymous2006-06-14 2:51
You need some sort of exhaust for propulsion in space. Period.
Keep in mind that the exhaust can be just light. You can strap a huge laser on your shuttle and turn it on, and that will cause you to move; the reason is because light has momentum. It's an exhaust because you're throwing that energy out the back of your shuttle.
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Anonymous2006-06-14 5:16
I wonder if you could rig something up using something that doesnt interact with normal matter usually...say neutrinos...
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Anonymous2006-06-15 4:46
Neutrinos are still matter genius, and it doesn't even make a difference because even if your exhaust is just electromagnetic radiation, it still carries away momentum.
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Anonymous2006-06-15 5:31
>>10
actually, the reason brought that up was both ordinary matter and light react with matter pretty intensly. neutrino's don't nearly as much, meaning the exaust would probibly be less-harmful. just that generating neutrinos presents an issue right now.
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Anonymous2006-06-15 23:21
>>11
Why would it matter what the exhaust does once it leaves the ship?
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Anonymous2006-06-16 2:02
>>8
But isn't light considered massless?
And if momentum = (mass)(velocity) where light's mass=0, how can it hope to impart any propulsion?
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Anonymous2006-06-16 3:42
Momentum of massless objects
Massless objects such as photons also carry momentum. The formula is:
p = \frac{h}{\lambda} = \frac{E}{c}
where
h is Planck's constant,
λ is the wavelength of the photon,
E is the energy the photon carries and
c is the speed of light.
people standing behind the exaust, mostly. with something propelled by neutrinos, you could launch it from earth without having to worry about destroying some city like you would with light. chemichal reactions, of course, have been done.
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Anonymous2006-06-17 1:06
>>1
Newton's 3rd law means that there will be no net forward motion.
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Anonymous2006-06-17 3:08
>>1 Look up perpetual motion machines, an interesting read. I like the random movement in a gas powering a pinwheel idea, which is a little like this one.
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Anonymous2006-06-17 18:49
Perpetual motion machines are impossible, plain and simple.
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Anonymous2006-06-17 18:58
>>18
Even if you use magic? Because there's a low-level spell I don't know that makes objects emit light FOREVER!