Keith Williams
The key point which you have never conceded is this is wrong:
we will never get to 100% because the exhaust gas is not sufficiently stiff to resist being accelerated rearwards.
F = m.a. For any given thrust, the acceleration of the exhaust gas varies directly as the inverse of its mass. Stiffness does not come into it.
In post 17 I replied saying:
Quote:
You are correct in saying that the mass is the measure of its inertia. We only need to look at Newton’s Second Law equation F = MA to see that.
In post 20 you then continued to attempt to convince me of something to which I had already agreed
...”agreed” except the very next word was "But...":
You are correct in saying that the mass is the measure of its inertia. We only need to look at Newton’s Second Law equation F = MA to see that. But Newton assumed that the bodies in question were free to move. And if for example, one of the bodies were moving around a pivot such as your hamster wheel, then the stiffness of the bearing would also affect the outcome.
Let’s imagine that we took your hamster wheel and added an adjustable friction brake to the pivot. With the brake fully off the hamster would accelerate the wheel up to some given speed and then maintain this speed for as long as it kept running. But if we gradually tight the friction brake while the hamster continued to run, the wheel would gradually decrease. At some point the friction would be sufficient to stop the wheel, and if the hamster kept running it would follow a vertical looped path inside the wheel. So although we did not ever change the mass of the hamster or the mass of the wheel we have completely changed the outcomes. In order to determine which situation (wheel spinning / hamster stationary or Wheel stationary / Hamster spinning) gave the better propulsion efficiency, we would need to know what the hamster was trying to achieve. And as neither of us speak hamster we can never know that.
The point of the hamster wheel analogy is that you can see it spin because the moment of inertia is very small compared to the Earth. Your response is proof (in the colloquial sense) that you didn't take the point, even though you now claim to have agreed – in which case the thousands of words you have written seem unnecessary.
This response typifies the approach which you have taken throughout this thread. When faced with comments with which you disagree you ignore them and simply restate the laws of motion.
I disagreed and made counter points. But it's true there was quite a lot to ignore too, some rambling strawmen plus a few errors I didn't bother with. If there's something in particular you want me to answer feel free. I have some more points I want to make anyway, your withdrawal won't change that. After all, as you wrote: "every day should be a day in school, so please go for it".
