chrismb wrote:I don't think you understand the issue of frame-specific entropy, then. For 'work' to be done, there has to be some capability for a change of state to occur 'exothermically', that is to say, entropy increases. If you have a well-defined (by position and momentum) set of particles then they have a given entropy, but only with respect to their inertial frame for it differs between frames. For example, if you were to take a look at a lump of granite, it is chemically very inert and all the SiOx consituents are thermalised and so it cannot do any 'work'. But only in its frame, for if it were actually a meteorite you were looking at, heading towards the earth at 30,000kph, then that meteorite-earth system now does have the capacity to do work. So you can't separate out inertial frames to see where 'work done' can go, or be subsequently made use of. If you invent an 'absolute universal frame' then what you are describing is a reducing entropy as the sum of all frames, which we presume to be falsifiable by our modern understanding of thermodynamics.
So now it's the
second law, then? You're dodging all over the map. What happened to relativity?
I personally think you should forget paulmarch's comment about reducing the temperature of the universe; it seems to be unhelpful...
Did you read this like I asked you to? I haven't been playing fast and loose with reference frames like you seem to be accusing me of; this works out fine (to first order) with a simple Galilean transformation:
93143 wrote:...from rest the energy associated with 0.1 m/s of delta-V is 0.005 J/kg. At 7.5 km/s, the energy associated with 0.1 m/s is about 750 J/kg. The key point is that the lower the velocity difference between an engine and its reaction mass, the lower the required energy output gets. This is the Isp principle.
The reaction mass is distant matter. Plenty of distant matter is moving at very close to whatever reasonable speed you want to go.
From the perspective of the drive, this means you do a small amount of positive work on that distant matter, causing it to move slowly in the direction opposite your thrust vector.
From the ground, the distant matter slows down slightly, doing a large amount of positive work on the already fast-moving M-E drive.
...paulmarch, have I really missed something critical here?
I will admit that the spinner idea seems to me that it might violate the entropy condition, but as I said in my original acknowledgement of this, I haven't done the math, and it's entirely possible I'm wrong. It's also possible, I suppose, that the M-E spinner acts as a kind of universe-wide Maxwell's Demon... but this has nothing to do with conservation of energy, which was your initial argument.
ltgbrown wrote:I still do not understand how energy is being extracted for net power. How does .035 N/w efficiency turn into a net power device?
Remember that a newton and a watt are not units of the same thing, and are thus not directly comparable. Then go revisit my earlier post where I calculated it out and see if you can understand the math. It's pretty basic; it shouldn't be hard.
The upshot is that if you can generate torque in the way you've described, you can run a generator with it, and with reasonably efficient M-E thrusters, the power required to produce the torque can be smaller than the power you get from the generator. The key requirement is that the speed of the thrusters at the edge of the device be high enough, since power is force times velocity. This means that the faster you spin the thing, the higher the gain becomes. Energy is not actually created; the M-E thrusters are getting it from the rest of the matter in the universe. As my quote above demonstrates, the faster the thruster moves, the more work is done on it by the force between it and the distant matter (again, P = Fv).
You can generate power this way with ordinary rocket engines too, but since you need to fuel them (and accelerate the fuel up to the flywheel speed) it doesn't come out over unity no matter how fast the flywheel turns, so this is simply a particularly impractical way to build a heat engine...