drumdude wrote: ↑Sat Aug 14, 2021 6:21 pmFor me, I get an intuitive understanding of how it works by watching this video, starting at 13:30Physics Guy wrote: ↑Sat Aug 14, 2021 2:54 pmSailing faster than the wind is weird, but part of the weirdness is in saying it that way. It makes you think of a square-rigged sailboat somehow out-sailing the wind, and that indeed will not work. Think of a windmill hooked to wheels on a track with gears, though, and it's obvious that you can use wind power to move straight into the wind, if you want. And indeed these bizarre faster-than-the-wind wind-powered vehicles are mounting rotors, not sails.
In fact they aren't just windmills, and what they are doing is not as obvious as that. They are not just absurd; in fact they actually work; how they work is quite tricky.
As with most physics puzzles, there are different ways you can think about this one. Here a big consideration is whether to think about everything in the reference frame of the ground, where the vehicle is moving, or from the reference frame of the vehicle, where the ground is running under the wheels like a conveyer belt. Most other physics conundrums have different perspectives in some way like that.
From each perspective there will usually be some parts of the solution that seem obvious while other parts are hard to notice. Also, which aspects of the situation are crucial and which are insignificant details is not obvious until you understand everything fully. So it's tempting to adopt one perspective and decide that the things that seem obvious from that perspective are crucial while the things that are obscure must be unimportant.
When people who have adopted different perspectives on the problem argue, they tend to thump the table about the points that seem clear from their perspective, and respond to the other person's points by just reiterating their own. This can make a physics argument look a lot like a religious argument. But there are two big differences.
Firstly, of course, in the physics case one can do the experiment. These DDFTW vehicles really do work in practice, so the problem is to understand how they work, not to dispute about whether they do. Once everyone accepts that they do work, however, exactly how they work can still be a dispute—and it's not just an academic dispute, because it may have implications for how to improve these vehicles or apply their principles in other ways.
So even after the first difference of experiment between physics and religion, the second difference remains important as well. In physics all the simple arguments from any perspective are just simplifications of a fully detailed theory that remains the same in all perspectives. So arguments from any perspective can be translated into the other perspective, with objectively perfect translation accuracy, if one is willing to go into enough detail. Sitting around the table with beer, nobody may have enough time or sobriety to do this convincingly; the pens and napkins will come out but the napkins will be too small and the diagrams will be crooked.
If people stand in front of a whiteboard the next day going at it hammer and tongs for as long as it takes, though, the truth will come out. After an hour or two or more, the disputants will have descended into such fine detail that they will have invented their own private language just for this specific discussion. If a third party arrives it will take them several minutes just to explain to the newcomer what they are saying. But at some point one of the disputants will say, "Oh. You were right." Or perhaps both will realise that neither was right.
At any physics conference you will find lots of little gatherings around whiteboards going through that kind of exercise. It's why we have conferences. The big auditorium lectures aren't nearly as important.
In theoretical physics it is always possible to zoom in to more detail, because if you really must, you can try to talk about what every single electron in every atom is doing. If you could do that successfully, you would necessarily resolve every problem. So zooming in to more detail is a reliable tool for resolving controversies. It can be time-consuming and hard. It strains brains, even brilliant ones.
My brain has not been brilliant enough so far to fully understand these DDFTW vehicles. From one perspective I can see pretty clearly how they can work, but from that perspective I can't see why they won't work to "sail" in dead calm. From another perspective I can see clearly why they can never sail in dead calm, but this second perspective is no help to me in seeing how they can work when there is some wind. So I can kind of cover all the bases, but only with different perspectives, and that is not good enough. I won't consider that I understand this problem properly until I can explain all of its features succinctly from a single perspective—and do that from any perspective.
I reckon I'm only going to be able to resolve the paradox that fully by going to a more detailed level, and that will take a few hours, for sure. I often burn up hours on tasks that looked at first as if they would be done in minutes, but these days it's hard to find time for anything that I know in advance will take hours, if it's not something I have to do.
Maybe when I retire.
https://youtu.be/yCsgoLc_fzI
It is essentially force multiplication just like you see with pulleys, gears, and levers.
Exactly. The little wheels vs the large propeller create a lever situation. The 2x4 on top of the wheel combination shows it perfectly.
