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

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IanB:
Due to the power of The Algorithm, I came across this very appropriate video just now. It is rather apposite to this thread.


electrodacus:

--- Quote from: Kleinstein on December 27, 2021, 11:55:27 pm ---You claimed the power would be the power needed to drive against the wind - I (and most others here) were in doubt of that. That is your theory that gives the wrong result !   I just enteres a very small speed and used the very basic force = power / speed  formula for a mechanical movement.

--- End quote ---

It is not my claim as in I did not discovered anything new.

Just imagine this.
You are stationary anchored to the ground.  You can chose to "lift the anchor" and your vehicle will be accelerated direct down wind or down stream (boat on a river). This power to accelerate is provided to you by the wind or stream of water but if you decide to drive swim upstream then you need way more power as you are going against the stream.
So while your vehicle in the wind is stationary or boat on a river is stationary relative to ground you are likely anchored.

Have you ever had the chance to swim in a river ?  What amount of power do you need to swim upstream compared to down stream ?   

IanB:

--- Quote from: electrodacus on December 28, 2021, 12:03:56 am ---Just imagine this.
You are stationary anchored to the ground.  You can chose to "lift the anchor" and your vehicle will be accelerated direct down wind or down stream (boat on a river). This power to accelerate is provided to you by the wind or stream of water but if you decide to drive swim upstream then you need way more power as you are going against the stream.
--- End quote ---

Here is the graph of power vs. speed:



If you want to drive upstream at a slow speed, then you need very little power, as you can see from the graph.

If the boat wants to go upstream at a tiny fraction of the speed of the current, it only needs a tiny amount of power.

(If you care about "anchor", imagine the boat is anchored by a rope, and it can go upstream by pulling on the rope. If the gearing on the pulley is low enough, it can go upstream with the power from a tiny little battery and a little tiny motor.)

electrodacus:

--- Quote from: IanB on December 27, 2021, 11:59:20 pm ---
That is the wrong answer. Maybe you would like to try again?

--- End quote ---

I will ask you the same thing as it is a decently good analogy.
Have you ever had the chance to swim in a river ?

gnuarm:

--- Quote from: electrodacus on December 27, 2021, 11:18:56 pm ---
--- 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.

--- End quote ---

How is the energy storage relevant?  If the vehicle continues against the wind indefinitely, it is moving against the wind.  Who cares if there are tiny variations in the speed?  This sort of storage of energy is not relevant to the issue.  At no time does the velocity fall below the wind speed.

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