It's a freakin' mind bender.
sure is. I was intruiged to see one trucking down the road and had that gut feeling 'something must be wrong', but it didn't seem actually spooky. Your cart making headway up a slope against the treadmill powering it is just mental! I suppose I haven't felt such disbelief-vs-awe since I was a small child and got my first Ifel-Tower with a giro on top. We get used to these things that at first appear miraculous and 'break the laws of physics'. Still, I'm not convinced yet.
To be honest I would like to believe that being right and being convincing would be far better than offering my qualifications - but I realize on the internet that's not always the case.
For me it's a part of the drip-drip of many clues that I guess we all weigh up in these situations. Others are the quality of your explanations, the quality of contrary POVs expressed, etc.. Still, I'm not convinced yet.
How'd you like me to post another 30 brainteasers that will do the same? At least when you get a few in, you start to realize that you can't always trust your intuition. Physical intuition is a GREAT tool, but it's a great lesson to learn that it's far from perfect.
It's fine by me if you'd like to post more, but don't exhaust yourself with all this. You seem to be putting a lot into just this one.
I assure you there's no groundbreaking engineering here - just a really fun and bizarre novelty (whose only practical use is to start internet pissing matches).
Ah, so you wanted to start one!
I wouldn't be so sure about the groundbreaking engineering question (but obviously you know the field). I doesn't have to be an undiscovered physical principle, just one that is very commonly overlooked, for opportunities to be missed in designing new inventions. It might not be a new mode of transport, but out of all these engineers who don't know about it, there might be a good few who would love to have it at their disposal.
Probably just displaying more ignorance here, but I wonder if there are patents that involve the principle. You say you weren't the first to discover it. Still, I'm....
Very unlikely. Perhaps it will indirectly lead to an internet forum troll filter.
No, I can't see that working, ever.
If you can get an electronic version, it should give me a Retrieve button, to go and fetch my posts after I've submitted really stupid ones. Oooh, and if you manage this with photons, you should be able to travel faster than light. Nice.
Oddly, yes and no. I laughed when my father suggested I publish it a couple of weeks ago. Clearly no one in the field would be fooled for a moment by such a silly brainteaser. Since then I've had religious discussions with PhD's and engineering professors that are absolutely certain it can't do what we observe it doing. As a result, I think it is worthy of a journal writeup. I've met with some folks and am just starting that ball rolling. We'll see how it goes.
Good. I wish you luck.
When I originally concieved of this I was somewhat proud of myself (only for the novelty of it). As it happens I'm far from the first to have thought of it, or even demonstrated it. Publishing this will almost certainly cause a stir only because even the experts fall so hard on both sides of the issue. But there will be no prize or award.
Well, that sounds like the right motive. It's fascinating, and would cause a stir and educate other scientists. Still...
Explaining it to people that find it hard to believe is fun. The bad mouthing - not so much.
Ah well. You gain some you lose some. Conservation of mood.
But our intuition tells us that "outpacing our power source" means outrunning the wind. But this isn't the case. We are immersed in this fluid. And this fluid happens to be moving in an advantageous direction to allow us to extract some energy. The paper and spool demonstrates this very nicely. Even as it moves along faster than the paper, there is still paper there to apply the necessary force to continue to motivate the spool.
Yes. But it breaks the law of conservation of prejudice, unfortunately. You didn't notice that.
In our theoretical example let's make those spoke sails in the form of a japanese fan that extends and retracts - normal to the flow of the wind.
Alternately, you could build a cart like I show that has a belt that goes all way around (above and below) the deck. The vanes extend on the bottom and fold down on top.
Sure. I could design them myself. It's just that lack of physics knowledge again - for all I know, even if I use gravity to close the vanes, or they do so by pressure against the air somewhere else in the system, or indeed, if they're represented by the constant pitch of a prop, yet somehow doing the same kind of thing, it could all cancel out and give you no advantage, or it could give a net gain sufficient to do the DWFTTW trick. I don't know. I won't know, perhaps until I physically handle something that does it, or I finally get all the bits of the jigsaw sorted in my mind. Thanks for helping.
Again, there is not minimum inherent work done here. We can make that work be arbitrarily small by using the most clever materials and techniques. Folding them normal to the wind doesn't inherently take any specific amount of energy.
I see. But it's not about the absolute measure, is it? Isn't it the question of, wherever that energy is extracted, whether the mechanics have to push negatively against something to do it?
I don't know if this is relevant, but I'll put the question and see. I woke up this morning with this new invention fully formed: I've taken your cart and squished it and also made it radially symetrical, so that instead of running along a flat surface, it runs in a cylindrical pipe. It has spring-loaded wheels in two whorls, three in front, three behind, so as to locate it centrally in the pipe and maintain contact with the surface, one or more of these geared to a prop in the same fashion as per cart. I guess that's clear enough to 'see' it, but I'll draw it if you like. In a lossless mechanical system, I guess we could ignore springs and clearances of prop against the pipe, but no matter. I presume that this also hasn't changed the mechanical scenario too much. We may have different constraints on the air - I have now confined the column, and pressure might be able to build up, say, where in free-flowing air I guess this has a sideways dissipative ability. But I also imagine that such a device located in a pipe with fluid flowing along it would behave very much the same as your cart, outpacing the fluid by some amount. Ok so far?
Now, imagine three identical pieces of pipe with the same fluid conditions, a steady flow, and into one we magically materialize the device (pipe A) and in the other, we pop the same mass without any mechanical advantages of the device (pipe B). A control, C has just fluid.
So my question was going to be where the extra energy comes from for A to have a mass crawling through the fluid, so to speak, faster than the fluid itself? If I compare it with B and C, there is another requirement of energy, too, to propel the mass at the same speed as the fluid. I imagine that from rest it would be accelerated by the fluid, so the fluid would lose energy. I think the mass would approach the fluid velocity and 'eventually' match it. To maintain the same flow rate, I imagine, would require more power from the pump driving the fluid.
But in A, the device is pushing back on the fluid, accelerating to (say) twice the speed of the fluid, and the force, I guess, must translate into a similar reduction in energy of the fluid, and/or more juice to the pump to maintain the same speed.
Here again I am faced with my bootstrap levitation question. I think that doing this has made me more able to say that the cart slows the wind it is immersed in (as would a cart being blown along without a prop). So I guess the question forming in my mind from this is: is it true to say that, although the cart moves faster than the general windspeed, measured in the carpark or whatever, it never goes faster than the wind relative to itself? Does it in fact slow the column of air it moves through proportionally to however much faster it manages to go?
I'm sincerely sorry if I am just being dim again. This does seem in essence like a repeat of my original 'objection' (although put less arrogantly, I hope). I am still having a problem with the idea of the energy source not being 'the wind', but 'the wind relative to the ground'. To me they are the same. They represent different origins to measure stuff by. If we consider ground as fixed, there is only wind to extract energy from, nothing else at all. If we start taking about squeezing the machine between the wind and the ground to extract more energy, we're starting to move origins, it seems to me. We end up trying to measure windspeed relative to the craft, and now we don't have the SAME wind-ground speed, because where the craft is, it is now propelling air backwards. If we measure THAT airspeed relative to the ground, it is proportionally slower. No???
You say:
But for a given gear ratio you can only exceed the true wind speed by a fixed percentage. Remember that this is extracting energy from the true wind over the ground - not the wind over itself. We could in theory increase the gearing and therefore the speed indefinitely, in a perfect (lossless) world. But in the real world there will be a real limit.
What do you mean by 'the wind over itself'? If I am travelling at 200 mph in a 1 mph breeze, what about the headwind of 199 mph? You seem to suggest that we could continue to accelerate in a lossless world (I want one of those) with super gearing, but how can you not be lumping the 199 mph headwind into the description of 'loss' here to still extract energy from a 1 mph ground-windspeed?
I'm sorry, but I keep coming back to my problem. Maybe you can help explain it with another expression of it. I understand (roughly) the idea of the tacking. It seems to me that a land yacht can gain more and more energy because it is moving across the wind, and has an inexhaustible supply of it to tap. It picks up momentum by actually slowing the wind, yes? But it doesn't matter, because it moves on to another bit of wind to the side. I can translate this to a prop blade moving across the wind, but here it passes back to its original position with the period of rotation. Now, it may be that in that time a new piece of air has arrived from the rear, when the cart is going at lower than windspeed, but
at windspeed it is now spinning through the same air as before, which it already extracted energy from and slowed.
Or maybe you can help me get beyond this by examining my earlier scheme (if you haven't done so already). If the cart on the treadmill slows rwt track (for whatever reason), its wheels turn slower, don't they? This was powering the prop, so doesn't it drop in power output? Doesn't that mean it doesn't move 'up' the tread as fast? Doesn't that give it less speed at the wheels? Etc. Of course, it's movement backwards through the air represents some kind of source of energy that might help it move forwards again, but...ugh?
Or this: A body in a stream of atoms, that's all we have (ok, next to stationary atoms). Atoms hit body. The body is mechanical and doesn't just get hit, absorbing energy to reach the speed of the passing atoms, but throws atoms backwards, changes their momentum. Still, to power whatever it is that's doing the throwing, it has to brace itself against something, (conservation again), and all there is to brace against is the same flow of atoms or the stationary ones. At atom-flow-speed, it has the motionless body of atoms next to it - how does it use that, or its relative velocity wrt the flow? That's now going at atomspeed backwards wrt the body and the flow. You can't shove a generator in the gap and let it wind up your speed, surely? Those 'stationary' atoms can only drag you.
If we have a wheel with the old vanes half speed below the axle. Isn't there something about the moment and pressure (I think someone mentioned this earlier), that means that even if the vanes are moving at v/2, and thus have a following wind of v/2, in order to increase the speed of the whole wheel (because it is rotating over the fulcrum of its contact with the ground?) would require more force than a v/2 wind can give it. If I push my bike wheel below the axle, it may go forward twice as fast as the point I'm pushing, but it's an inefficient lever compared with pushing the axle.
