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Electroboom: How Right IS Veritasium?! Don't Electrons Push Each Other??

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electrodacus:

--- Quote from: Naej on July 07, 2022, 12:04:18 am ---The power is taken from the wheel in the sense that there is a significant friction on the tires, and this is the key for understanding how the car accelerates.
At the same time there is larger force forward given by the propeller (when you accelerate).
As I said before, it's a propeller not a turbine.
If wind speed+1m/s=vehicle speed, you can take 130 W from the wheel and get a large thrust from the propeller.
For example, if the propeller gets 10 kg/s of air, it can accelerate it to 2.7 m/s and get a thrust of 27 N.
If the vehicle speed is more than 5 m/s this is more than tire friction and your vehicle accelerate.
You get a large torque, which is why the vehicle is shaped like this.

Energy conservation is correct in a closed system. If you don't define the system, you can easily say wrong things, like here. And if you don't define the reference frame, ditto.
Bottom line is: both the atmosphere and the Earth are big, so there's a huge amount of energy in wind and if you neglect the annoying drag, you can go as fast as you want.

There are plenty of things going faster than the wind.
For example:
- all wind turbines.

It works in the same way as sailing boats which go faster than the wind, you just need to change direction regularly (tacking), and a rotor does this in an almost perfect way.

--- End quote ---

You are a smart guy based on the other comments I saw from you.

I'm fairly bad at explaining things but I will try my best.

Let's start with the simplest wind powered vehicle just wheels and a sail driving directly downwind (very important it is directly downwind as even a sail vehicle can exceed wind speed if it drives at an angle).
 
I guess you will agree that wind power available to this vehicle (ideal case no friction involved) is 0.5 * air density * area * (wind speed - vehicle speed)3
Highest wind potential energy is when vehicle speed relative to the ground is zero.
This wind potential energy can be all converted to kinetic energy in ideal case so ideal vehicle speed can get at most at wind speed.

Now no matter how you modify the vehicle the air particles can only interact by colliding with equivalent area of the vehicle.

So now let just say vehicle is at half the wind speed and just 16.2W of wind power is available to this ideal vehicle no friction.
You can use this 16.2W to increase the vehicle kinetic energy (increase vehicle speed) or you can decide to take that extract energy from the wheels let say to power a 16.2W incandescent light bulb.
In this case since you take 16.2W from the wheels to power the 16.2W lamp the vehicle will no longer accelerate and just maintain the same speed (half the wind speed in this example).
Now you can replace that incandescent lamp with whatever you want. Can you make the vehicle accelerate faster than it already did before deciding to take those 16.2W from the generator wheels ?
Say you install an electric driven propeller and supply those 16.2W to that and also let say the propeller is 100% efficient. Can you get more than 16.2W worth of thrust ?

I hope you agree you can not get more power out than you get in.
Somehow people think either propeller's or gearboxes are magical devices that can output more power than they get in.
Power you take at the wheel is wind power so taking that subtracts from wind power available to vehicle to accelerate.
Without adding an energy storage device no vehicle can exceed with speed powered by the wind.   

electrodacus:

--- Quote from: dunkemhigh on July 07, 2022, 12:21:27 am ---
Well, at this point one has to ask "What the  hell is the question you're asking!?!?" Clearly, the total power available is the wind acting on the surface, which is the equation you provided. There is no other power, so it is that which provides for the acceleration and everything else.

Also, I think you've failed to remember that the test vehicle had the prop blades feathered until it reached close to wind speed, at which point they were manually adjusted to provide appropriate thrust. I think you should consider that a significant clue.

However, what is very clear is that even when you get precisely what you ask for, you don't live up to your promise. There is no point or use in discussing anything with you because you are blind and immune to anything except whatever your mind has made up.

--- End quote ---

Both my equation and the one you provides shows that vehicle can not exceed wind speed unless and energy storage device is included.
Just put some real numbers in the equation you provided and see for yourself that your equations shows no wind power above wind speed.

PlainName:

--- Quote ---Both my equation and the one you provides shows that vehicle can not exceed wind speed unless and energy storage device is included.
--- End quote ---

Rubbish. The one you provided shows there is zero power at wind speed, but the proper version that I provided doesn't show that. It does show that power will reach zero but not the speed at which that happens. That will be dependent on how much power is taken for the prop and what thrust the prop provides.

From the equation as it stands, you cannot know if the vehicle will even reach wind speed or exceed it. To suggest otherwise means you are pre-judging based on only your bias, without thinking what the equation actually says.

electrodacus:

--- Quote from: dunkemhigh on July 07, 2022, 01:09:53 am ---
--- Quote ---Both my equation and the one you provides shows that vehicle can not exceed wind speed unless and energy storage device is included.
--- End quote ---

Rubbish. The one you provided shows there is zero power at wind speed, but the proper version that I provided doesn't show that. It does show that power will reach zero but not the speed at which that happens. That will be dependent on how much power is taken for the prop and what thrust the prop provides.

From the equation as it stands, you cannot know if the vehicle will even reach wind speed or exceed it. To suggest otherwise means you are pre-judging based on only your bias, without thinking what the equation actually says.

--- End quote ---

This is the equation you provided
Pw = (0.5 * air density * area * (wind speed - vehicle speed + wash speed)3) - Pp

You added "wash speed" and Pp
If both values are zero you get zero wind power at vehicle speed equals wind speed.
If "wash speed" is any value higher than zero then wind power will be zero before vehicle even gets to wind speed and the same happens with Pp

Just use 6m/s for wind speed and same for vehicle speed and area can be 12 to keep calculation simple. Add any values you think are realistic for Pp and "wash speed" and let me know what the wind power is is when vehicle speed equals wind speed.

PlainName:

--- Quote ---If both values are zero you get zero wind power at vehicle speed equals wind speed.
--- End quote ---

Yes, and...?

[Quick diversion: they won't both be zero because the thing is moving, hence turning the wheels, hence sucking power, etc.]

But let's just recap what this is about:


--- Quote --- All you need to convince me is provide an equation describing the available wind power to Blackbird.
--- End quote ---

That's what you got. No more, no less. You can try the faithful distraction technique of diving into irrelevant details and hope someone will start arguing those, but that doesn't change anything. The equation is either good or it isn't. Plug in whatever values you like, but they're not going to change what the equation is saying.

So, what is wrong with it? It includes the important stuff yours conveniently left out - there is a big propeller sucking power by causing drag on the wheels, so even if you don't like this equation, your version is even worse.


--- Quote ---Add any values you think are realistic for Pp and "wash speed" and let me know
--- End quote ---

Completely irrelevant diversion. Settle on the equation and then you can think about values. You don't change things to suit the result you've already decided upon.

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