Technorati Tags: ddftw, bozos,
So, as I said in the edit to my previous post about the wind-driven cart, I seriously blew it. The folks who pointed out the similarity of the cart to a tacking sailboat were absolutely correct. The guys who built this cart, and recorded the demo were absolutely right, and I was stupidly wrong, in multiple ways. First of all, I thought this was a really simple system. I couldn't possibly be more wrong about that - this is anything but simple; in fact, it's a remarkably interesting and elegant demonstration of how complicated and counterintuitive fluid dynamics can be. Second, I completely misunderstood the simple mechanics of the device; I originally thought that the propellor was spinning in the opposite direction - and I completely missed it when people repeatedly tried to explain that error to me. And third, I completely screwed up my own mathematical model of how something like this works.
So - to repeat: the guys who did the demo of this are clearly not bozos; the only bozo in this situation is me, for screwing it up so badly, on so many levels. I sincerely apologize for calling them bozos and mocking them. I made a whole series of really stupid errors, and took an unreasonably long time to recognize that fact.
It should be obvious that there's some way to go downwind faster than the wind, because as so many people pointed out, sailboats do it. It was frankly stupid of me to even argue about this - it's really pretty boneheadedly obvious. The question never should have been "can it be done?", but rather just "does this device do it?"
And the answer to that is "Yes". This thing does do it. It's not magic, it's not perpetual motion. In fact, it's really astonishingly simple, once you realize that the behavior of things moving through air is quite different from the simple rigid system that it appears to be equivalent to.
In this post, I'm going to try to do two things:
- Explain the faulty reasoning that led me to think it couldn't work, and why it's wrong.
- Explain why the thing really works.
In another post later this week, I'm going to try to explain why I think the mathematical element is so important. There's a ton of people who've got devices that really look convincing, and that have really convincing arguments for why they should work; only they don't, because they've missed something.
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