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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: cbutlera on September 01, 2021, 07:22:33 pm ---
My apologies, but I thought it was obvious. I am a passenger in a normal aeroplane flying at normal cruising altitude at 200 m/s.  I stand up from my seat and walk down the aisle of the aeroplane towards the front of the aeroplane at 1 m/s, relative to the aeroplane.  I weigh 70 kg.

To an observer on the ground (using the ground frame of reference), by getting up and walking along the aisle, I have accelerated from 200 m/s to 201 m/s. To this observer on the ground, I have increased my kinetic energy by 14,035 joules.  Where did this energy come from?

--- End quote ---

I did not understand because your proposal demonstrates nothing.
You are not between two mediums you are just on one medium that moves relative to the ground. So you walking inside the plane requires energy that you will provide by burning some extra calories while in motion at 1m/s and as soon as you stop walking you will be back at 200m/s.
This vehicle discussed here has no other energy source other than the wind (there is the energy storage that is why it works for a bit) but the claims made by people is that it can run forever since they do not consider the existence of the energy storage.
Also your kinetic energy only increased by 35J (35Ws) relative to the airplane and that increase you mentioned relative to ground was provided to you by the plane. So while you where accelerating forward at 1m/s you increase the airplane fuel consumption by a bit. But when you returned to your seat you compensated by slightly reducing the fuel consumption.
I know for a large panel this increase and decrease in fuel consumption as you where acceleration inside the plane are so insignificant that can not even be measured they are provided by the plane and not by you. Else you will be fairly hungry after this small few second walk.
PlainName:

--- Quote ---That is because you do not understand the difference between my diagram and a flipped vehicle.
--- End quote ---

Undoubtedly! Nor your explanations, such as they are. So, just demonstrate it with an actual experiment. Imagine: no more misunderstandings, talking at cross-purposes, undecipherable diagrams - it will just be obvious once you show us it happening.

Why don't you?
PlainName:

--- Quote ---even if I show it is now working you will think I did something to trick you
--- End quote ---

But, obviously, we would never suspect you of doing that when we show you an actual experiment demonstrating the opposite!
cbutlera:

--- Quote from: electrodacus on September 01, 2021, 07:43:12 pm ---
--- Quote from: cbutlera on September 01, 2021, 07:22:33 pm ---
My apologies, but I thought it was obvious. I am a passenger in a normal aeroplane flying at normal cruising altitude at 200 m/s.  I stand up from my seat and walk down the aisle of the aeroplane towards the front of the aeroplane at 1 m/s, relative to the aeroplane.  I weigh 70 kg.

To an observer on the ground (using the ground frame of reference), by getting up and walking along the aisle, I have accelerated from 200 m/s to 201 m/s. To this observer on the ground, I have increased my kinetic energy by 14,035 joules.  Where did this energy come from?

--- End quote ---

I did not understand because your proposal demonstrates nothing.
You are not between two mediums you are just on one medium that moves relative to the ground. So you walking inside the plane requires energy that you will provide by burning some extra calories while in motion at 1m/s and as soon as you stop walking you will be back at 200m/s.

--- End quote ---

I am not talking about operating between two mediums.  I'm taking a step back and considering a simpler case, which will turn out to be very relevant to the original more complex case.

I ask you again, to the observer on the ground (in my thought experiment above), I have increased my kinetic energy by 14,035 joules.  Where did this energy come from?
electrodacus:

--- Quote from: cbutlera on September 01, 2021, 07:55:31 pm ---
I am not talking about operating between two mediums.  I'm taking a step back and considering a simpler case, which will turn out to be very relevant to the original more complex case.

I ask you again, to the observer on the ground (in my thought experiment above), I have increased my kinetic energy by 14,035 joules.  Where did this energy come from?

--- End quote ---

I may not have been very clear.  In your tough experiment there are two sources of energy both contributing to your increase in kinetic energy.
Out of that 14035J you contributed 35J and the plane contributed with 14000J.  You used some of your stored energy from food while plane used kerosene or whatever that plane was using for fuel.
This will not apply to vehicle having a single energy source (wind energy).
Of course a vehicle traveling in same direction as the wind can exceed that wind speed if it has access to another energy source like say a human pedaling or a battery or as it is the case a pressure differential energy source.
If experiment is done for just a limited amount of time so that energy source is not all used up you will get to the wrong conclusion that wind alone powers the vehicle but if you run the experiment a bit more you will see the entire picture with vehicle decelerating below wind speed once the stored energy is used up.
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