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| Mess with your minds: A wind powered craft going faster than a tail wind speed. |
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| bdunham7:
--- Quote from: electrodacus on December 12, 2021, 09:11:30 pm ---You can have Force without having power means vehicle speed and kinetic energy will not change. Power is a more than Force especially in this context. --- End quote --- You can have force without power, but do you understand under what specific conditions that can happen? |
| Kleinstein:
The correct explaination does not need energy storage, as it works in a steady state. I think the idea of energy storage is more like a futile attempt to cast doubt in what the experiments show. So it may still help to show, that there is no significant energy storage in the prop driven vehicle, that helps: I don't see how the propeller would be a usefull way of energy storage: The energy in the flywheel action increase when the vehicle goes faster. So it can not be used to accelerate (unless you constantly change the gearing). It is actually slowing down the acceleration. The pressure field around the prop is also expected to get stronger when the prop goes faster - so also more like additional energy needed to accelerate. In addition the pressure field would dissipate quite fast (at the speed of sound) as there is no back wall. So the energy is gone in fractions of a second. This also gives an idea that the energy in the compressed air would be pretty small, good for a fraction of a second at most. Elastic energy in the drive train (e.g. the chain or twist of a shaft) would also up with more force and thus for most cases with higher speed. With a relatively solid drive train the stored energy is pretty small. With the force of the drive and less than 1 m of elastic range, thus would only power the vehicle for less than 0.5 seconds at a speed of 1 m/s (and correspondingly shorter at higher speed). The vehicle with wheels (e.g. beam on top if the wheel version from Derek) work even easier than the ones with the prop - even less change to have some hidden energy storrage there. The vehicle with the rubber band does some slip stick (not slap-stick :-DD). I don't consider the rubber band helping, it is more like making it more complicated and not working as well. It would also work with a chain drive instead, and than without the slip-stick part. The rubber band does a little energy storage. Hoever the vehicle only oscillates between standing still (which corresponds to the speed of the wind) and going forward (corresponding to faster than the wind). So this shows that it is harvesting energy when going at the speed of the "wind". |
| fourfathom:
--- Quote from: electrodacus on December 12, 2021, 09:47:42 pm ---The treadmill model is being held not dropped on the treadmill. During those few seconds the treadmill charges all energy storage devices available on the vehicle the multiple flywheel devices and the pressure differential. --- End quote --- No, while the vehicle is being held on the treadmill it is reaching equilibrium. If after release it was burning off stored energy it would instantly begin to slow down. Instead, it accelerates. |
| electrodacus:
--- Quote from: IanB on December 12, 2021, 09:50:54 pm ---Air being a compressible fluid is not a means of energy storage, as the moving air in the propeller stream is less dense (lower pressure) than the still air in the surroundings. This can be learned in every physics or aerodynamics textbook as Bernoulli's principle. There is no way that the lower pressure air can "push" from behind. --- End quote --- A propeller can create a pressure differential in air and that is where energy is stored. See below graph https://en.wikipedia.org/wiki/Axial_fan_design |
| electrodacus:
--- Quote from: fourfathom on December 12, 2021, 11:32:57 pm ---No, while the vehicle is being held on the treadmill it is reaching equilibrium. If after release it was burning off stored energy it would instantly begin to slow down. Instead, it accelerates. --- End quote --- If it has stored energy say that 0.07mWh I calculated that are needed to accelerate that vehicle from 0m/s to 1m/s. Of course those 0.07mWh of stored energy will accelerate the vehicle if is a slow acceleration or fast is irrelevant it will still have enough stored energy to get to 1m/s and in the video the vehicle did not get close to 1m/s. It probably needs minutes at that slow acceleration rate to use all the stored energy. Things can be changed to show deceleration before getting to the other end of the treadmill like adding enough weight to the vehicle. |
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