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| Mess with your minds: A wind powered craft going faster than a tail wind speed. |
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| gnuarm:
--- Quote from: electrodacus on December 27, 2021, 08:56:37 pm --- --- Quote from: gnuarm on December 27, 2021, 08:49:17 pm ---I didn't say anything about a brake. I said zero motion. Work is force over a distance. You can push as hard as you want against an object and if it does not move you have done no work on it. You may have sweated up a storm, but that's internal inefficiencies. Actually, I can lean into a wall without any real effort on my part. I'm just using my weight and gravity to provide the force. I would construct some examples to show you there is no work being done, but it really gets tiresome that you just can't understand the basic concepts. So you think that holding an object in a fixed position against a force requires performing work on the object? Do you understand what is meant by "performing work" in the physics sense? If the wind is blowing, and something is pushing against the object, but not moving it against the wind, is the something doing work? --- End quote --- I remove the brakes from a bicycle you can sit on that and then in a 230km/h head wind and see if you can have a low speed close to zero relative to ground. In fact you can keep the brakes and you will still have no change against 230km/h wind. A wall is anchored to ground. --- End quote --- I see what bdunham7 meant... Ok, how about a 20 km/h wind? I don't even need to work. I just have to keep pressure on one pedal which I can do easily without doing work on the bicycle. No motion, no work. Do you agree with that? I debated with myself over the stationary vs. infinitesimal speed issue realizing that either way you would find some inane point to argue about. 230 km/h head wind is pretty much reductio ad absurdum. |
| electrodacus:
--- Quote from: gnuarm on December 27, 2021, 10:37:01 pm ---I see what bdunham7 meant... Ok, how about a 20 km/h wind? I don't even need to work. I just have to keep pressure on one pedal which I can do easily without doing work on the bicycle. No motion, no work. Do you agree with that? I debated with myself over the stationary vs. infinitesimal speed issue realizing that either way you would find some inane point to argue about. 230 km/h head wind is pretty much reductio ad absurdum. --- End quote --- Yes 230km/h is absurd that is why I selected that speed. I set 1km/h for the bike so it is low speed but possible while keeping your balance then increased the head wind in the calculator until power required was equal with 300W as 300W can be done by a fit person. Obviously power needed is not 300W else you will see electric bikes with 300W motor and 230km/h top speed. 20km/h (5.55m/s) head wind is no challenge as power need to slyly move forward will be 0.5 * 1.225 * 0.408 * (5.55)^3 = 42W so basically a breeze. And yes you can just stay still by leaving your body weight on the pedal at just 20km/h head wind. |
| IanB:
--- Quote from: electrodacus on December 27, 2021, 08:32:20 pm ---No vehicle can move directly upwind powered only by wind without energy storage (Fact). --- End quote --- What would you say if someone showed you a wind powered vehicle that moves directly upwind without energy storage? |
| gnuarm:
--- Quote from: electrodacus on December 27, 2021, 10:44:54 pm --- --- Quote from: gnuarm on December 27, 2021, 10:37:01 pm ---I see what bdunham7 meant... Ok, how about a 20 km/h wind? I don't even need to work. I just have to keep pressure on one pedal which I can do easily without doing work on the bicycle. No motion, no work. Do you agree with that? I debated with myself over the stationary vs. infinitesimal speed issue realizing that either way you would find some inane point to argue about. 230 km/h head wind is pretty much reductio ad absurdum. --- End quote --- Yes 230km/h is absurd that is why I selected that speed. I set 1km/h for the bike so it is low speed but possible while keeping your balance then increased the head wind in the calculator until power required was equal with 300W as 300W can be done by a fit person. Obviously power needed is not 300W else you will see electric bikes with 300W motor and 230km/h top speed. 20km/h (5.55m/s) head wind is no challenge as power need to slyly move forward will be 0.5 * 1.225 * 0.408 * (5.55)^3 = 42W so basically a breeze. And yes you can just stay still by leaving your body weight on the pedal at just 20km/h head wind. --- End quote --- Ok, so if the user is stationary in a 20 km/h head wind, how much power is required to maintain this position? If you come up with any answer other than zero, you can't explain how a brake works. The brake can maintain this position into the 20 km/h wind while dissipating no power. A rider can do the same thing by simply standing on the pedal preventing it from rising up. One foot on the ground for balance, one foot on the pedal to maintain position. No power transfer. ZERO You seem to have already agreed that this is correct. In that case you must agree there is no power transfer at the wheels for a stationary bike/car/blackbird and that the equation that predicts power at the wheels based solely on the wind relative speed must be wrong. |
| electrodacus:
--- Quote from: IanB on December 27, 2021, 11:14:40 pm ---What would you say if someone showed you a wind powered vehicle that moves directly upwind without energy storage? --- End quote --- That is not possible so I will show him where energy storage is. Maybe for this particular case I will ask him to take a video with a high speed camera to notice how the movement is not constant but it fluctuates as energy storage is charged and discharged. |
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