GIThruster wrote:That seems to me a long winded reply. The thrust efficiency of any thruster is a figure of merit that exists for all thrusters. For a chemical thruster, it is the thrust over the energy from the reaction products burned over time. It is for stationary thrust only. Taking this figure of merit and pretending it is invarient when it is not, will always yield this absurd math error. It does not matter what kind of thruster one has.

Also, because v is relative, any thruster can be started at a v just 1 second before it goes overunity in said calculation. This means that all thrusters would go overunity. It does not matter that it does or does not have propellant, how much propellant, etc.

Again, the mistake here is trying to do relativistic calculations the wrong way. You have a constant that is not invarient. The thrust efficiency is for a stationary thruster ONLY. Once the thruster starts to accelerate, that constant varies because it is not invarient. If instead of allowing it to vary as it would with a proper transformation, you hold it as invarient, you get these absurd conservation violations. This is becasue you did the math wrong.

They are not doing the math wrong. They are doing it

*incompletely*.

Kinetic energy of a single body is not a real energy. Kinetic energy is inherent in a velocity

*difference*. Think about it (remembering that energy is the capacity to do work).

**In order to get conservation of energy to work with an accelerating thruster, all you have to do is account for the energy transferred to or from the exhaust.** This is trivial for a rocket engine (though with external feed, such as with the flywheel example, you have to take into account the energy required for the propellant to catch up with the rocket engine before use), but for an M-E thruster you need to define the "exhaust" rather precisely to get the right answer.

I'm not convinced chrismb has done this, but his scenario is at least internally consistent and breaks no conservation laws (at least, if it's the scenario I think it is based on skimming his pompously-named "final word" post). Given the small scale of the experimental results to date, and my lack of precise knowledge of the power system parameter traces during experiments, it could even be right. I've ordered the book, and will take a look at the details to see if I can refine my understanding.

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Of course the thrust/power ratio of a rocket engine is invariant with velocity. That's how the Oberth effect works. If this were not true, a rocket would violate Galilean invariance long before it got anywhere near fast enough to worry about Lorentz covariance.

The only way your argument makes sense is if you are including total energy transferred to the rocket in your ground reference frame in the "power" calculation. This is frankly a silly way to do it because that "power" is not seen in the rocket's frame of reference, and only falls out when you do the energy accounting correctly for a 'stationary' reference frame as I describe above. The actual power exerted by the engine is the net gain in kinetic energy over time of the rocket+exhaust combination, which is not the same as the gain in kinetic "energy" over time of the rocket alone and can easily be less. It is also frame-independent.

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If you disagree with my assertions regarding energy accounting and thrust/power in a rocket, be aware that you are disagreeing with an expert. I'm not a physicist, but I have two degrees in mechanical engineering and am finishing up one in aerospace, so Newtonian mechanics is as natural as breathing to me. And while I have only a modest working understanding of relativity, I do understand what sort of problems you need it for; this specific subproblem is not in that category.

painlord2k wrote:In your math do you computed the changing mass of the magic ship?

The changing dimension in the same direction of the vector of the thrust?

The slowing down of the time inside the ship?

None of those matter. Relativistic effects are mathematically unrelated to the over-unity calculation and therefore cannot be used to counter it. There's plenty of headroom for a thruster of reasonable efficiency to go locally over-unity without going relativistic. The argument falls down, not on relativistic grounds, but on energy accounting grounds - the extra energy comes from the rest of the observable universe.

And, of course, there's the question of whether the thrust/power ratio of the thruster remains constant in all inertial frames. From the nature of the case I expect it should, but it may not.

*Did you think about the possibility your rotating engine could not work using Woodward effect?*

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So the tangential component of the force developed by the drive will go down as the wheel spin faster and will become zero at some point..Then if you force the wheel to spin faster, it will act as a brake.

Again, the mathematics of this is unrelated; your description does not appear to be accurate, but even if it were the problem is unconstrained; you can always specify a wheel big enough that the centripetal acceleration is much smaller than the accelerations in the M-E device (actually, for any reasonable thrust efficiency it's probably difficult not to).

Also again, if the thrust/power ratio of the thruster depends on its velocity relative to a velocity-invariant collection of distant reaction mass, as suggested by chrismb, these cases basically work just like the engines we're familiar with - cars, rockets, etc. - and cannot result in even an entropy-condition violation (conservation of energy is safe regardless).