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Down wind faster than the wind

Brian-M said:
Assuming they're bumping and jostling you as the pass, you end up being pushed forwards, the same as what happens when you're traveling along at less than wind speed.

If you're a walker in a corridor full of people walking at a slower speed, assuming you're bumping and jostling them as you pass, you end up being slowed down, the same as what happens as when you're traveling faster than wind speed.

If you're a walker in the corridor full of people walking at the exact same speed as you, then they have no effect on your speed, neither slowing you down nor speeding you up, the same as what happens when traveling at wind speed.

There is no wind resistance at wind speed. Can you understand this?
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Assuming they're bumping and jostling you as the pass, you end up being pushed forwards, the same as what happens when you're traveling along at less than wind speed.
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But, if I am slower than the traffic, how do I make progress forward unless I pass someone? It's crowded, I will probably have to push someone out of the way to do that, and that will slow me down.

Perhaps the two effects work together.

If I am trying to travel through one of those childrens' rooms full of colored balls, what difference does it make if they are all traveling at the "same" speed? And no quite the same speed?

You can't alter a frame of reference. You can only change what reference you're looking at things from by converting the figures over.
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So why bother then.

If you are using belt speed as your frame of reference, and you change the speed of the belt, you can either convert your numbers over to look at it from the frame of reference from the new belt speed, or you can continue to look at it from the original belt speed (relative to the new belt speed).

Applying the figures from one frame of reference (original belt speed) to a new frame of reference (new belt speed/ground speed) without converting the figures results in nonsense gibberish.

If you stop the belt, the car next to the belt is still traveling the same speed relative to the original belt speed. Nothing changes.

No, I'm saying because there is no difference which wall you bounce the ball off, even though the house on the equator is moving at a tremendous speed relative to the motion to the earth, that throwing a house at a ball is exactly the same as throwing a ball at a house, as far as the interaction between the house and the ball is concerned.

Throwing a rock 100mph from a bridge at the windshield of a parked car causes exactly the same damage as dropping a rock from a bridge onto the windshield of a car driving at 100mph.
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Only as far as the interaction is concerned:
You say a person hitting a stationary car at 60mph, is the same as a car hitting a stationary person at 60mph.

If the person hits the car, how far will the car move?
If the car hits the person, what then?
Will the person in each case, have the same velocity and kinetic energy?
Which interaction will last longer?
 
ynot said:
You cannot travel faster than the wind by tacking downwind. You can only travel faster than the wind by tacking against the wind - http://www.physclips.unsw.edu.au/jw/sailing.html
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Thank you, look at the diagram at "Why are eighteen footers always sailing upwind?". The downwind component of the speed vector is greater than the windspeed. Oopsie.

// CyCrow

ETA: sol made the same point. It's not just iceboats, but fast sailboats as well.
 
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CyCrow said:
Thank you, look at the diagram at "Why are eighteen footers always sailing upwind?". The downwind component of the speed vector is greater than the windspeed. Oopsie.

// CyCrow

ETA: sol made the same point. It's not just iceboats, but fast sailboats as well.
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And this large scale phenomenon, works for small propeller-driven carts?
 
humber said:
So why bother then.
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I won't bother trying to explain anything to you anymore. I hope mine and other explanations have helped some lurkers gain an understanding. You are just going in circles at this point, with poorly worded and meaningless questions. Everything needed to understand the device is here in this thread.

// CyCrow
 
Brian-M said:
If the cart is traveling at windspeed, there is no wind relative to the cart to turn the propeller. Ergo, the wind is not turning the propeller.

When the cart is moving downwind at wind speed, the air is stationary relative to the cart, and the ground is moving rapidly under the wheels.

When the cart is stationary on an indoor treadmill, the air is stationary relative to the cart, and the ground is moving rapidly under the wheels.

Where is the difference?

In both cases, the ground passing under the wheels.
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The difference is that in the treadmill example the energy is obviously coming from the treadmill. Were is the energy coming from however in the road example if it’s not coming from the wind on the propeller?
 
jsfisher said:
...except the propeller is geared to turn the wheels the other way.
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It’s unclear from the video exactly how the propeller is geared to the wheels but the propeller certainly appears to be turning the opposite way than it should if it was being turned by the wind. I hadn‘t noticed that before as I was looking more at the basic principals involved than the model.

In both video demonstrations the vehicle appears to be being accelerated solely by the wind created by the spinning propeller. The treadmill is obviously providing the energy in that example but were is the energy coming from in the road example? The propeller is not getting it’s energy from the wind and it appears to be getting it via the wheels from the vehicles movement along the ground. The only effect I can see the actual wind having is that the vehicle has less air résistance in it’s direction of travel. Other than that I can’t see that the wind plays any part at all in the motion of the vehicle. As it is impossible for a vehicle to accelerate purely from it’s own momentum I smell a rat!

The vehicle obviously has remotely controlled steering and brakes and therefore carries some form of battery power source. I strongly suspect that the vehicle is being powered by a remotely controlled hidden motor driven by hidden batteries.

Unless of course someone can explain were the vehicle gets it’s energy from to move along the road. If it’s not from the wind on the propeller - how?
 
It's been explained numerous times in the thread ..

The vehicle obviously has remotely controlled steering and brakes and therefore carries some form of battery power source. I strongly suspect that the vehicle is being powered by a remotely controlled hidden motor driven by hidden batteries.
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Then how is the version on the treadmill being powered ?
 
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jsfisher said:
...except the propeller is geared to turn the wheels the other way.
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It is the first case. The way that it is used in the treadmill video, shows it being used the other way. The treadmill forces this condition. That is what you do not realise.
 
CyCrow said:
I won't bother trying to explain anything to you anymore. I hope mine and other explanations have helped some lurkers gain an understanding. You are just going in circles at this point, with poorly worded and meaningless questions. Everything needed to understand the device is here in this thread.

// CyCrow
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Not directed at you, so why did you?


Again,

CyCrow said:
Yes. Any reason it shouldn't?

// CyCrow
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It goes to the nature of turbulence, and the scalability of dynamic systems.
 
ynot said:
The difference is that in the treadmill example the energy is obviously coming from the treadmill. Were is the energy coming from however in the road example if it’s not coming from the wind on the propeller?
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You are catching on. I asked that if the belt was the wind, why was the propeller not driven from the road?
If the air is the air, where is the ground?

"Oh, the wheels of course"

They have this "frames of reference" business.
 
sol invictus said:
That's just... false. See here for example: http://www.nalsa.org/Articles/Cetus/Iceboat%20Sailing%20Performance-Cetus.pdf

Look at the diagrams. Iceboats can sail downwind, at angles very close to straight downwind, MUCH faster than the wind.
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Yes I was wrong. It is possible to travel faster than the wind downwind but only by tacking (moving at an angle to the wind) not directly with the wind. That’s my current understanding anyway and it could also be wrong.

ETA - In other words, you can travel faster then the wind but not in the exact direction of the wind unless you are using conserved energy from tacking and that won't last unless you tack again.
 
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ynot said:
It’s unclear from the video exactly how the propeller is geared to the wheels but the propeller certainly appears to be turning the opposite way than it should if it was being turned by the wind. I hadn‘t noticed that before as I was looking more at the basic principals involved than the model.

In both video demonstrations the vehicle appears to be being accelerated solely by the wind created by the spinning propeller. The treadmill is obviously providing the energy in that example but were is the energy coming from in the road example? The propeller is not getting it’s energy from the wind and it appears to be getting it via the wheels from the vehicles movement along the ground. The only effect I can see the actual wind having is that the vehicle has less air résistance in it’s direction of travel. Other than that I can’t see that the wind plays any part at all in the motion of the vehicle. As it is impossible for a vehicle to accelerate purely from it’s own momentum I smell a rat!

The vehicle obviously has remotely controlled steering and brakes and therefore carries some form of battery power source. I strongly suspect that the vehicle is being powered by a remotely controlled hidden motor driven by hidden batteries.

Unless of course someone can explain were the vehicle gets it’s energy from to move along the road. If it’s not from the wind on the propeller - how?
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It is driven forward by the wind, but they way it is used on the treadmill, leads you to think that it works the other way.
 
ynot said:
The difference is that in the treadmill example the energy is obviously coming from the treadmill. Were is the energy coming from however in the road example if it’s not coming from the wind on the propeller?
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From the road.

Look - imagine, instead of a cart on a road, a zeppelin floating in the air. Suppose at some altitude there's an interface between two layers of the atmosphere, with one moving with respect to the other. So to someone at rest in the lower level, the upper level is moving rapidly (to the left, say), while someone facing the same way but at rest in the upper level would say the lower level is moving rapidly to the right.

Now, imaging our zeppelin is floating at this altitude. It can lower a sail or propeller up, down, or both. We're interested in the case where it's moving at the speed of the upper layer (like the wind for the cart). Then the layer below it is moving rapidly to the right. Question - can the zeppelin use that motion to move to the left; i.e. into the wind below it? The answer is clearly yes - it's easy to design things that move into the wind.

But if you agree, that's it - you agree something can move downwind faster than the wind (because that's what the zeppelin will do with respect to the upper layer). Just replace the lower layer with ground, and the lower sail/propeller with wheels, and you're there.

If you don't agree, I can give you plenty of examples of things that move into the wind.

Does that help? The only thing that ever matters is relative motion, and the energy is always coming from there.
 
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humber said:
Not directed at you, so why did you?
Again,
It goes to the nature of turbulence, and the scalability of dynamic systems.
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The quote was too good to pass up. As for scalability, you are moving the goalposts. You claim the concept is impossible in general, not at any particular scale. It is harder to get good efficiency as you scale aerodynamics down, so the fact that it warks at small scale is even better.

// CyCrow
 
ynot said:
It’s unclear from the video exactly how the propeller is geared to the wheels but the propeller certainly appears to be turning the opposite way than it should if it was being turned by the wind. I hadn‘t noticed that before as I was looking more at the basic principals involved than the model.
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This is an essential part of the basic principle of the model. If the person behind the cart were to pick it up and hold it so that the propeller was in the wind stream and the wheels could turn freely, the propeller would turn clockwise and the wheels would turn backwards. When it runs on the ground, it is pushed forwards by the wind, forcing the wheels to turn on the ground. The movement of the wheels forces the propeller to turn anti-clockwise. The action of the propeller against the air causes the cart to accelerate.

In both video demonstrations the vehicle appears to be being accelerated solely by the wind created by the spinning propeller. The treadmill is obviously providing the energy in that example but were is the energy coming from in the road example? The propeller is not getting it’s energy from the wind and it appears to be getting it via the wheels from the vehicles movement along the ground. The only effect I can see the actual wind having is that the vehicle has less air résistance in it’s direction of travel. Other than that I can’t see that the wind plays any part at all in the motion of the vehicle. As it is impossible for a vehicle to accelerate purely from it’s own momentum I smell a rat!
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In both cases, the energy is coming from the difference between the speed of the air and the speed of the ground. It makes no difference if we consider the air to be moving and the ground to be fixed, or if we consider the air to be fixed and the ground to be moving. Look up the principle of Gallilean Invariance.
 
ynot said:
Yes I was wrong. It is possible to travel faster than the wind downwind but only by tacking (moving at an angle to the wind) not directly with the wind. That’s my current understanding anyway and it could also be wrong.

ETA - In other words, you can travel faster then the wind but not in the exact direction of the wind unless you are using conserved energy from tacking and that won't last unless you tack again.
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You're correct for ordinary sailboats. But once you admit you can go downwind faster than the wind at any angle, you're almost there. In principle it doesn't cost any energy to jibe (it's actually called jibing, not tacking, when you turn with the wind rather than into it). So you can jibe back and forth and go as straight downwind as you like, with an average speed much faster than the wind. In principle you could attach two sail or ice boats together, each jibing back and forth in a crossing pattern, so the whole contraption moves straight downwind.
 
humber said:
Please show me the textbook, that states that a car stationary upon a 60mph treadmill, has the same kinetic energy as the same car traveling at 60mph along a road, whereas the one on the floor next to the treadmill does not.
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The textbooks will tell you that kinetic energy is not an absolute property. Kinetic energy is a function of velocity (1/2 mv2), and velocity is a relative property.

If the car on the floor and the car on the treadmill have the same mass, then they have the same kinetic energy relative to any inertial reference frame. Relative to the floor, both these cars have zero kinetic energy. Relative to a frame of reference going at the same speed as the treadmill, both cars have kinetic energy as defined by the familiar formula. This is equivalent to the kinetic energy of the car going at 60mph along a road when measured in the frame of reference where the road is stationary. The kinetic energy of the car travelling at 60mph is zero when measured in a frame of reference going at the same speed as the car.
 
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