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Electroboom: How Right IS Veritasium?! Don't Electrons Push Each Other??
electrodacus:
--- Quote from: Naej on July 13, 2022, 10:38:08 pm ---I told you before, in the wind reference frame the ground has kinetic energy. It's obvious but you thought I were a fool.
In the treadmill model, which is nothing more than blackbird in the wind reference frame, the treadmill is providing the energy (and I'm afraid I want to add: obviously).
Yes and wind turbines too. Some claim they will run for decades and have excess energy to power other things. Crazy right? It must violate the conservation of energy. :-DD
--- End quote ---
The treadmill model is the equivalent of blackbird after the vehicle is above wind speed.
As soon as you release the vehicle from you hand the treadmill provides no power to vehicle.
Wind turbine is stationary so air particles will hit the blades. If you put the wind turbine on a vehicle and set the vehicle speed so that exactly equals wind speed there will be zero wind energy available to that wind turbine.
electrodacus:
--- Quote from: Nominal Animal on July 13, 2022, 10:26:36 pm ---Equilibrium models cannot properly describe the physical phenomena at hand –– suitable craft going downwind ––, because in the real world, wind speed is not constant, nor does it have a perfectly stable direction.
When you simplify the situation enough so you can apply equilibrium physics, you're essentially discussing how a toy on a rail in a perfect wind tunnel behaves. I don't think that is useful; it's not what happens in real life.
Consider a wind pattern where you have some base wind speed X, with a roughly sinusoidal component on top (although the exact shape or frequency does not matter, as long as the changes occur in relatively short timeframes, say on the scale of seconds, and they're symmetric, not affecting the average wind speed –– this is more or less quite typical wind behaviour). For now, let's assume it stays in the same direction.
Instead of a fabric sail, let's imagine you have wanes that act like a one-way valve: when the craft velocity is below wind speed, the wanes catch the wind, and when the craft velocity is above wind speed, the wanes let the wind pass through mostly unhindered. It won't be perfect, but all we're looking for here is asymmetry.
Even on a fixed straight track in a wind tunnel, that craft will reach a speed that exceeds the average wind speed. If there were no losses, it would reach the maximum repeated wind speed. Some, perhaps most of the time, it is exceeding the wind speed, only getting additional power from the gusts, "peaks".
It is quite analogous to the behaviour of charge in a capacitor.
The second thing is the wind direction. When sailing on sea, you don't get the best efficiency by catching the wind like a parachute: you get best speed by using your sail like the wing of an airplane (very similar flow profile, too). You can make a pretty good sailboat by making a vertical wing (like the ones on aeroplanes, but vertical) that you can rotate around its vertical axis. Now, I do not claim to know or understand fluid dynamics (physics sub-field that deals with the flow of liquids and gases) nor sailing, but it should be obvious that wind direction, even small changes from directly downwind, hugely affect the situation.
In particular, even if the craft itself had wheels running in a direct line, it could have a cylindrical arrangement for its "sails", rotating vertically, so that in effect its sails would be jibing even if the craft itself was going straight.
Again, an equilibrium condition examination (where the craft is traveling exactly at wind speed with any such arrangement not rotating) is not useful, because the equilibrium state is a point that only exists in carefully controlled situations, and not in practice.
Plus, pressure differentials in the wind make the fluid dynamics even weirder.
As to the equilibrium scenario discussed ad nauseatum above, I have no opinion, because it is quite uninteresting to me, being overly simplified and unrealistic.
--- End quote ---
You try to make similar claims as Alex (that university professor in Derks second video).
While all those where valid points it was not able to explain the top speed of the vehicle as it was higher than peak speed during that record test.
Also the much more controlled treadmill vehicle could not be explained that way.
The treadmill vehicle drives against treadmill when released and there is no wind as it is indoor and treadmill speed is fairly constant while the vehicle travels in the opposite direction to treadmill pushed by the earlier created pressure differential.
You can see this as a vehicle with a generator/motor and a capacitor.
While kept with th hand on treadmill the capacitor is charged to some fixed voltage (pressure differential) proportional with the treadmill speed so if you keep the vehicle longer it will not get extra energy stored.
Once you release the capacitor (pressure differential) provides power to motor to accelerate the vehicle forward and cover frictional losses.
The treadmill can not apply a force against the vehicle after you release as if that was the case vehicle will move backwards so in the direction that treadmill is moving as there is nothing to push against (ignoring stored pressure differential).
If your hand was sensitive enough will be able to feel a force in the direction the treadmill moves when you first touch the vehicle to treadmill then that force will at some point be equal with created pressure differential and after that the pressure differential will provide higher force so you will release the vehicle that will be pulled and pushed by that pressure differential created by the propeller.
Of course that pressure differential drops and you can measure how acceleration rate drops fairly fast just not fast enough over the short length of the treadmill to see how it stops accelerating and moves backwards.
But taking a video from the side you will be able to calculate the acceleration rate to say three sections of 30cm and see how acceleration rate decreases as pressure differential drops.
You can add weight to vehicle based on that calculation to show how vehicle stops accelerating before it reaches the end of the treadmill.
That seems the simplest proof but I'm sure people will still deny that energy storage being used up is the reason.
Naej:
--- Quote from: electrodacus on July 13, 2022, 11:43:35 pm ---
--- Quote from: Naej on July 13, 2022, 10:38:08 pm ---I told you before, in the wind reference frame the ground has kinetic energy. It's obvious but you thought I were a fool.
In the treadmill model, which is nothing more than blackbird in the wind reference frame, the treadmill is providing the energy (and I'm afraid I want to add: obviously).
Yes and wind turbines too. Some claim they will run for decades and have excess energy to power other things. Crazy right? It must violate the conservation of energy. :-DD
--- End quote ---
The treadmill model is the equivalent of blackbird after the vehicle is above wind speed.
As soon as you release the vehicle from you hand the treadmill provides no power to vehicle.
--- End quote ---
Wrong.
--- Quote from: electrodacus on July 13, 2022, 11:43:35 pm ---Wind turbine is stationary so air particles will hit the blades. If you put the wind turbine on a vehicle and set the vehicle speed so that exactly equals wind speed there will be zero wind energy available to that wind turbine.
--- End quote ---
Yes. Completely and utterly irrelevant. Wind mills provide more power that you put in (0W).
You're trying to disprove what thousands of physicists understand, and what was experimentally proven. Obviously you're just making mistakes. So stop lying to yourself about your understanding of energy and start learning.
electrodacus:
--- Quote from: Naej on July 14, 2022, 12:05:15 am ---Yes. Completely and utterly irrelevant. Wind mills provide more power that you put in (0W).
You're trying to disprove what thousands of physicists understand, and what was experimentally proven. Obviously you're just making mistakes. So stop lying to yourself about your understanding of energy and start learning.
--- End quote ---
If you think treadmill powers the vehicle explain to me how it will do so. It will push against what ?
Why is the fact that a wind turbine traveling at wind speed produces nothing ? It just shows that there is zero wind power when vehicle speed equals wind speed direct down wind.
If thousands of physicist think that a direct downwind vehicle is powered by wind while above wind speed they should find a different job.
I can consider myself and expert in energy generation and energy storage so I have a very good idea of what energy is.
Your only understanding is based on the results on some incomplete experiments.
The blackbird excuse was that it was running out of road and needed to stop and the treadmill is way to short to see the vehicle slow down fully.
But you can see in any video how the rate of acceleration slows down.
You still did not provided a mathematical proof (nobody did). You showed an equation that was not only wrong but also predicted zero wind power when vehicle speed equals wind speed.
Not to mention that equation was your invention as nobody ever uses that equation for anything.
While the wind power equation I provided is used by basically everybody in a large range of applications.
Want to know how much wind power a sail vehicle has to be able to calculate how fast it accelerates you use that equation.
Want to know how much a wind turbine will produce again the same exact equation.
Want to know the power needed to overcome drag for any vehicle you use the exact same equation.
The range of applications is huge and it includes both versions of blackbird.
All you have is words and you are unable to make any sort of predictions.
Nominal Animal:
--- Quote from: electrodacus on July 13, 2022, 11:59:29 pm ---You try to make similar claims as Alex (that university professor in Derks second video).
--- End quote ---
No, that's just what I know when trying to model physical phenomena. My own scientific field is molecular dynamics modelling software and their development –– i.e., I'm a toolmaker more than I use those tools to do research ––, and this sort of thing, or oversimplified models and trying to find the correct complexity level where things are still understandable and simulatable, but not so simple that they no longer reflect reality, is a daily encountered problem.
Like I said, I am not interested in the equilibrium case. To me, it's like investigating automobile fuel consumption by assuming that all roads are straight without intersections and all travel at the posted speed exactly. In the real life, different types of vehicles' fuel consumption varies very differently due to repeated accelerations and decelerations, which is the reason why fuel mileage is usually reported separately for "city driving" and "long-distance driving": one being constant acceleration and deceleration, the latter with relatively stable speeds. Those who teach economical driving, always emphasize how big of a beneficial impact keeping to a constant speed makes.
To put it more simply, the case where the vehicle is traveling at exactly the speed of wind is not interesting.
Instead, divide the examination into two: One, when the vehicle is traveling slower than the speed of wind. Parametrise the scenario, and especially examine how acceleration changes as the vehicle speed approaches wind speed. Two, do the same examination, but in the case where the vehicle is already traveling faster than the speed of wind. Next, using the parameters (coefficients and such) you established, find out if and when the vehicle already traveling faster than the speed of wind can keep a nonnegative acceleration (ie., zero or positive).
The equilibrium case, where the vehicle has exactly the same speed as the wind, has zero acceleration, and has no exploitable energy storage, just doesn't happen in nature: it is an unstable state, and will always fall into one of the above two cases, sooner or later.
If, and only if, it turns out that the vehicle has always nonpositive acceleration when already traveling faster than wind, will that unstable state always fall to the lower speed side, and only then is it impossible for that vehicle to travel directly downwind faster that the wind. If you can find a mechanism or model and parameters, where the vehicle can keep a nonnegative acceleration while already traveling faster than wind, then that vehicle can keep traveling faster than wind almost indefinitely (barring similar unstable points, possibly an infinite number of them, as the exactly-same-speed-as-wind case).
So, as unintuitive as it might seem, the entire scenario seems to depend on exactly how the vehicle behaves when it is already traveling faster than wind directly downwind. In my mind, this is well in the realm of fluid dynamics; and indeed if a simple propeller-like arrangement can achieve that, the actual underlying mechanism is almost certainly more interesting than just flywheel-like energy storage.
I wouldn't trust a treadmill (either way!), because the static charge buildup in the belt can cause all kinds of wonky stuff. Depending on the materials, it can act like a big but not very good Van De Graaff generator, for example.
--- Quote from: electrodacus on July 13, 2022, 11:59:29 pm ---I'm sure people will still deny that energy storage being used up is the reason.
--- End quote ---
I'm not making any such claims, for or against. I am saying you are looking at the issue from the completely wrong angle.
The exact point where the vehicle speed matches wind speed is an unstable point state, which will immediately change. It is not interesting or useful to examine it, at least not before you have some kind of models that describe the two different situations around that state, depending on the speed.
I'm not saying anyone is cheating, either, but it would be easy to do, even unwittingly. You might make a very lightweight vehicle, but use heavy natural rubber wheels, which would definitely behave like an energy storage (flywheels, literally). A model that can describe multiple different such vehicles is the way to go.
Note that since the faster-than-wind-speed case is critical, it is not sufficient to show one model that works that shows it cannot be done; that only proves that that vehicle cannot do it. Considering sail boats (that can jig faster than wind nearly-downwind), I suspect it is possible, certainly possible enough to do research on, but I wouldn't be overly surprised to find out it would be unfeasible somehow either, say requiring a 1m long but 100m wide vehicle, for example.
Some kind of vertically rotating wane system would be what I'd look into myself, simply based on existing sailing techniques.
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