General > General Technical Chat
Mess with your minds: A wind powered craft going faster than a tail wind speed.
bdunham7:
--- Quote from: electrodacus on September 03, 2021, 04:10:07 pm ---I did not meant something else wall needed to be able to absorb the 9Ws else it will no longer be called a wall after the impact.
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Again, your arguments and suppositions easily reduce to absurdities, but for some reason you don't see it. An inflexible wall cannot absorb or provide any energy. It can provide a reaction force sufficient to stop the car, but no energy is exchanged between the wall and the car. Now if you try to bob and weave by saying the wall is not infinitely rigid, then you need to do more calculations. If you do, you will find that any actual energy exchange is miniscule.
Edit: And reflecting, I think the reason my mind allowed me to type 'power' when I meant 'energy' is that there actually is enough data to calculate the power provided by the wall--zero, the same as the energy. So I'll take back my point.
--- Quote ---But what about my other replays where I say power in and out of the system is a better/simpler way to predict if vehicle will slow down or accelerate. Looking at the balance of forces is not useful as those are forces at the wheel / propeller not the forces acting against the vehicle since vehicle is between two isolated mediums that have different speeds.
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That's just nonsense. If the wheel and propeller are fixed to the vehicle, as they are at least on the x-axis, then forces acting on them along that axis will act on the vehicle through reaction forces. Perhaps you don't understand what a 'force' is?
bdunham7:
--- Quote from: cbutlera on September 03, 2021, 04:26:08 pm ---Are there any of Newton's laws that you agree with?
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That Newton guy was just another idiot professor who made a lot of mistakes. Principia Mathematica is a hoax!
electrodacus:
--- Quote from: cbutlera on September 03, 2021, 04:26:08 pm ---So you are saying that the rate of change of momentum of a body over time is not just proportional to the net external force. It also depends on what that force or those forces are acting against.
Are there any of Newton's laws that you agree with?
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You are used with a single medium but this vehicle is between two mediums. So if you take 10W from one medium and use that to push against the same medium there is nothing to gain but you think that pushing on another medium that is at different speed gives you some extra and that is not the case.
10W put in to propeller will provide you 7W of thrust to vehicle (assuming that 70% efficiency) so vehicle will slow down if there is nothing else to help.
Ideal case taking 10W from the wheel for 1 second results in vehicle kinetic energy being 10Ws less. So if you take all this 10Ws and put it in to ideal propulsion pushing against another medium you get back what you lost in kinetic energy nothing more.
So now you can look at speeds and say wheel speed is 5m/s it means breaking force was 2N
And if say the other medium you pushed against only had 2.5m/s you will have needed 4N to be able to push with 10W for 1 second and get the vehicle kinetic energy back to where it was.
You see the 4N is higher than 2N and you think vehicle will gain speed but that is not the case and in ideal case the vehicle will just be able to maintain speed.
The problem is you are confusing the force at the wheel with forces acting against the vehicle.
Using Power only or Force and speed needs to provide you the same exact result if you interpret what happens correctly.
The Power equation is hard to mess up so is clear you wrongly understood what force at the wheel or propeller means in this case and that is different from force acting on the vehicle as vehicle travels on one medium takes energy from there and pushes using that energy against another isolated medium.
IanB:
--- Quote from: electrodacus on September 03, 2021, 05:12:42 pm ---The Power equation is hard to mess up
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Apparently it is really easy to mess up, as you keep doing so with your treadmill example and the nonsense conclusion that the cart cannot move from left to right when powered by the treadmill.
It is clear that if the G wheel can pick up power then the M wheel can receive power. If the M wheel can receive power, then it can equally well be made to turn clockwise or anti-clockwise (it just depends on the gearing). If the M wheel turns clockwise the cart will move from left to right.
There is nothing at all preventing the M wheel from turning clockwise. If it receives power, it can turn.
electrodacus:
--- Quote from: bdunham7 on September 03, 2021, 04:34:16 pm ---
Again, your arguments and suppositions easily reduce to absurdities, but for some reason you don't see it. An inflexible wall cannot absorb or provide any energy. It can provide a reaction force sufficient to stop the car, but no energy is exchanged between the wall and the car. Now if you try to bob and weave by saying the wall is not infinitely rigid, then you need to do more calculations. If you do, you will find that any actual energy exchange is miniscule.
Edit: And reflecting, I think the reason my mind allowed me to type 'power' when I meant 'energy' is that there actually is enough data to calculate the power provided by the wall--zero, the same as the energy. So I'll take back my point.
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Wall is fixed to the ground so that energy is transferred to earth. When vehicle accelerated it has pushed against earth accelerating the earth in opposite direction then when vehicle hit the wall all that energy was put back in to earth in opposite direction to initial acceleration.
Vehicle had 9Ws of kinetic energy before hitting the wall and 0Ws after. So where do you think that 9Ws disappeared ?
--- Quote from: bdunham7 on September 03, 2021, 04:34:16 pm ---That's just nonsense. If the wheel and propeller are fixed to the vehicle, as they are at least on the x-axis, then forces acting on them along that axis will act on the vehicle through reaction forces. Perhaps you don't understand what a 'force' is?
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You seems to be the one not understanding that force at the wheel (or propeller) is not the same with force against the body of the vehicle.
Think about a gearbox only that is 2:1 ideal so no friction.
I'm on the input side putting 1N and you are at the output side and will need to put 2N so that gearbox is in equilibrium no movement.
have you got the equilibrium part ? There is a huge difference in forces but no movement in any direction.
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