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Mess with your minds: A wind powered craft going faster than a tail wind speed.
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electrodacus:

--- Quote from: Kleinstein on December 15, 2021, 09:21:56 pm ---Going with 1 km/h against a heat wind of 35 km/h would need the force of going 36 km/h with no wind (irgnoring wheel friction and similar other power needs) with only 1/km/h instead of 36 km/h this would be 1/36 of the power needed for 36 km/h with zero wind. So taking the graph below to get a number, this for be bit below 300 W for 36 km/h and some 0.8 W for 1 km/h.

Other than for a rough number the chart is not really helping.

--- End quote ---

You need 300W to cycle at 36km/h with no wind and also 300W to cycle at 1km/h with a 35km/h head wind.
electrodacus:

--- Quote from: fourfathom on December 15, 2021, 09:24:26 pm ---You can push against a brick wall with lots of force, but no work will be done, so there's no power.
If the wind pushes against a vehicle with a the wheels locked and not rolling, no work will be done, so there's no power.
But if the wind pushes against a vehicle and a motor used to keep the wheels from rolling, there's definitely force, but the motor will also burn Watts to keep the wheels from rolling.  Watts is power.

And this actually has nothing to do with the reality of the demonstrated sustained DDWFTTW vehicles.

--- End quote ---

If you have no energy storage (like a spring between you and the wall) plus mechanical brakes you will need the power to maintain that force on the wall.
Yes if the wind pushes against a vehicle and vehicle is not moving no work is done but if it moves even at super low speed work will be done.

All of you seems to have some misconception about this that is why I insist. Once you get this you will understand why direct downwind faster than wind is impossible without energy storage. Same as direct upwind without energy storage is also impossible tho that is a fairly different problem.
Kleinstein:
The low speed case has no direkt relevance for the fast downwind case, but is shows that the way electrodacus thinks about power and force is totally screwed up. I still had hope he may realize that the 600 W for moving at a snails speed in the wind is obviously wrong.

Even for someone more used to electricity it should be clear that the mechanical power is speed times force.
For the vehicle to move it is about overcoming the opposing forces. There is no opposing power, as the power has no geometric direction.


--- Quote from: electrodacus on December 15, 2021, 09:43:52 pm ---You need 300W to cycle at 36km/h with no wind and also 300W to cycle at 1km/h with a 35km/h head wind.

--- End quote ---
That is absoulutely nonsense. It may be bit windy to drive a bike, 1 km/h is more like very slow walking and walking against the wind is still relatively easy.

Instead of using a bike, maybe consider a sail pulled by a rope. How about the power when using pullies ?  Is there anything magic in the fore caused by the wind that makes it different from other forces ?
bdunham7:

--- Quote from: electrodacus on December 15, 2021, 09:42:03 pm ---That is where you are wrong. The problem is basically the same.  Why do you think 300W are needed constantly to maintain that speed ? Is the air drag and you have that if you are cycling at 36km/h with no wind or at 1km/h with a 35km/h head wind. Same drag so same amount of power required.

--- End quote ---

The relative wind speed produces, as you say, the same force.  That force, multiplied by the speed of the bicycle, is the power required.  The power required is not the same in each case.


--- Quote ---All of you seems to have some misconception about this that is why I insist.

--- End quote ---

The people that have this 'misconception' comprise a pretty large group.  Ask some people you trust as experts, you'll be shocked at how many are in that group.

Why don't you 1) consult a physics textbook  2) ask someone qualified that you will actually believe  3) write to a few physics professors and see if they'll reply or 4) devise some sort of experiment that either you can do or a workable example where the results of your calculation are falsifiable?

I've tried to explain this to you many different ways and it just doesn't sink in.  I assure you I'm correct here--something I rarely assert definitively.
thm_w:

--- Quote from: electrodacus on December 15, 2021, 09:43:52 pm ---You need 300W to cycle at 36km/h with no wind and also 300W to cycle at 1km/h with a 35km/h head wind.

--- End quote ---

Not according to this: https://www.omnicalculator.com/sports/cycling-wattage
Its ~10W at 1km/h vs ~300W at 36km/h
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