Down wind faster than the wind

[ynot]

This is a wind powered craft that purports to travel directly down wind faster than the wind powering it.

It has also been posted on mythbusters.
http://forum.mythbustersfanclub.com/index.php/topic,12948.0.html

In essence the prop and wheels are directly connected through a drive belt. I defended the idea on physicsforums but unfortunately spork (the OP poster) wouldn't refrain from rants about being attacked and the thread got locked twice. This guy spork made his own version.
http://www.youtube.com/watch?v=1BRvYZd81AQ&fmt=18

Why I think it works:
It wasn't presented as perpetual motion and I agree that it's not. The source of energy is well define by the difference between wind speed and ground speed. This is regardless of the motion of the craft due to that difference being maintained by a direct belt connection between the prop and the wheels. With a constant power source at a given wind speed the velocity is limited only by the friction/wind resistance on the craft itself via Newton's first law.

My debate with spork concerned how the power was distributed through craft and the effects that had on efficiency. I could well have been wrong on some points of the wind powered version. However, the specifics in that regard are likely determined by prop to wheel ratio and prop efficiency. There is a difference in the treadmill case and wind powered case irrespective of the validity of the Galilean relativity argument.

What do you think? Will it work and why?

This Spork demonstration is like jumping off the ground and claiming you can levitate as it only considers a “successful” part of a total sequence.
If the person didn’t hold the vehicle stationary on the belt until it gained enough propeller speed to move against the direction of the belt it would never do so. If the belt was accelerated from being stationary to begin with and the vehicle was not restrained, the vehicle would always travel with the belt to some degree (due to the friction between the belt and wheels) and the vehicle would never gain enough propeller speed to move against the direction of the belt.

I the belt was long enough in the clip shown the propeller would loose power to the friction between the belt and wheels and the vehicle would always end up moving with the belt.

The vehicle is only temporarily moving against the direction of the belt using stored energy in the same way that a person that jumps is only temporarily levitating.

ETA - Just read the text at the start of the Spork video - DOH!

 

[Brian-M]

No it is not, Myriad. When a car is driven at any velocity above zero, the car must do work to make progress against that resistance. This does not happen on a treadmill ! Where is the wind?
It is not a matter of adding up velocities, because they are real objects that have mass and so forth. I understand the diagrams, no problem.

No, no, no! (Unless you mean the friction of the wheels, bearings, etc, but all these apply on a treadmill too.)

If a car is traveling at the same speed as the wind there is, by definition NO WIND RESISTANCE.

Wind resistance is a result of pushing through the air. If you're traveling at wind speed downwind, you are not pushing through the air, consequently there is no wind resistance.

To take the ball from zero to, say the 10mph it achieves,when it hits the wall, requires the application of force to accelerate it to that velocity.

To do the same, to accelerate a house to the same velocity, requires a much greater level of force. Not only that, they will have different levels of kinetic energy when that velocity is reached.

Hmmm.... a house on the equator is traveling East at 1037 mph due to the rotation of the earth. Do you think that throwing a ball at the East side would yield a different result from throwing it at any other side?

The only thing that matters here is relative velocity.

No? Do you really not see the difference? If a car on a belt says it is doing 60mph, but standing still, and there is no wind, that that is "the same". I mean literally the same?

Yes. Yes it is. Driving 60 mph downwind on the road with a 60 mph tailwind requires the exact same amount of energy as driving a car on an indoor treadmill belt moving at 60 mph.

Why stop there? The light reflected off the body work is going at lightspeed, so the relative "velocities" is lightspeed +/- bit.
Humber

Measuring the relative speed of light was attempted in the now famous Michelson-Morley experiment. (And repeatedly ever since.) This experiment is possibly the most famous, and most revolutionary experimental failure in history.

The fact that light speed is not relative overturned Newtonian physics, and inspired Einstein to come up with a new theory of physics to replace it.

I said earlier that this device is explainable with Newtonian physics. The speed of light isn't.

1. The "no drag" at windspeed idea, is a falsehood.
2. The rolling resistance of a vehicle on treadmill is much lower than that of a vehicle doing work against a load.
3. The argument assumes itself as a premise
4. The vehicle must get from zero to windspeed, a period of time in which it will
certainly experience drag.
5. See Ynot's post

Nothing to say about the treadmill?

Is it my turn to use this icon yet?

 

[humber]

This Spork demonstration is like jumping off the ground and claiming you can levitate as it only considers a “successful” part of a total sequence.

It can actually run longer, because the momentum in the propeller tends to keep things running long enough for it to pick up a little more to keep it going.
Generally, though, it would end up being dragged back.

Yep, there you go. Incontrovertible evidence that a vehicle can reach beyond windspeed.

DOH! is an apt conclusion.

 

[ynot]

It can actually run longer, because the momentum in the propeller tends to keep things running long enough for it to pick up a little more to keep it going.
Generally, though, it would end up being dragged back.

Yep, there you go. Incontrovertible evidence that a vehicle can reach beyond windspeed.

DOH! is an apt conclusion.

I always wonder if people that do these experiments are deluded or deliberate cons. Simply leaving the vehicle on the belt until the stored energy was spent would reveal the truth.

 

[humber]

.
Wind resistance is a result of pushing through the air. If you're traveling at wind speed downwind, you are not pushing through the air, consequently there is no wind resistance.

Brian-M,
What will happen if you are a walker in a corridor full of people passing by at a greater speed?

Yes. Yes it is. Driving 60 mph downwind on the road with a 60 mph tailwind requires the exact same amount of energy as driving a car on an indoor treadmill belt moving at 60 mph.

And the difference being that the car on the floor next to the belt, does not have a belt spinning its wheels.
Stop the belt. They are the same. Must be. The wind that wasn't there has gone too.

Hmmm.... a house on the equator is traveling East at 1037 mph due to the rotation of the earth. Do you think that throwing a ball at the East side would yield a different result from throwing it at any other side?

Because you think there is a difference between one wall and the other, throwing the house at the ball is "exactly" the same?

Now, you can't mean that. Not literally. I know you don't think that you can actually compare a house being thrown at a ball like that....But a car standing still can still be going 60mph

 

[humber]

I always wonder if people that do these experiments are deluded or deliberate cons. Simply leaving the vehicle on the belt until the stored energy was spent would reveal the truth.

The really astonishing thing, is that they believe (it appears to be belief) that this treadmill is the equivalent of a windtunnel.
A car on a similar belt, with a belt speed of 60mph, IS traveling at 60mph

 

[jsfisher]

The really astonishing thing, is that they believe (it appears to be belief) that this treadmill is the equivalent of a windtunnel.
A car on a similar belt, with a belt speed of 60mph, IS traveling at 60mph

You keep saying this. It still isn't true. Motion is relative to some reference. You are implicitly taking the Earth's surface as your reference, but there is nothing that requires that.

Stop trying to contradict the whole notion of relativity. The theory is not likely to be over-turned in this forum.

 

[sol invictus]

The cart moves directly down wind, I think? Tacking devices move across the wind, forcing the craft to travel further ( that's one of a number of possibilities). The velocity can be increased, because Work=force x distance,
so there is no paradox. Direct wind faces a direct resistance to motion that presents a barrier at terminal velocity, that would require over-energy to breach.

Total nonsense. A long while back modified gave an example of a device that sails directly downwind faster than the wind (two iceboats jibing back and forth connected by a bar). More simply, it's trivial to travel at an angle downwind much faster than the wind - and I mean with your speed in the wind direction faster than the wind, not just your total speed.

So there manifestly cannot be a law of physics that's violated by this (not that you've ever given an example of what such a law might be).

So the wind, the real wind, is modeled by you in your analysis as one of those vectors?

No idea what you mean. The wind speed is a vector field which we are assuming to be constant in both space and time for these purposes.

If that is not the case, and it takes only the energy of the wind relative to the ground, then that is the Newtonian model, and so failure is therefore proscribed.

Why? You simply make unsupported assertions. I already gave a summary of the forces, using standard Newtonian analysis, which indicates there is a force pushing the device to accelerate downwind when it's moving at the speed of the wind.

But it's not that simple, because a car on a dyno or belt, is said to be equivalent to the real item in wind, when it is not. A car, on a dyno or belt, that remains in position as seen by the operator standing along side, has no kinetic energy. It has no velocity.

OK, I'm tired of arguing. You're wrong, you're contradicting every physics book, wikipedia, the collective knowledge of nearly all other posters in this thread, logic, and the evidence of your eyes. On top of that you refuse to put your money where your mouth is.

There's a word for people like you - it's "troll".

 

[humber]

You keep saying this. It still isn't true. Motion is relative to some reference. You are implicitly taking the Earth's surface as your reference, but there is nothing that requires that.

Stop trying to contradict the whole notion of relativity. The theory is not likely to be over-turned in this forum.

No, but it is taking a good beating

ETA:
Seeing that you are speaking for Einstein, perhaps you can tell me if he would agree with this;

If you pick up a car, and put a belt under its wheels, and run the belt to 60mph, that is in no way different from driving in a 60mph tailwind.

 

[Brian-M]

Haven’t had time to read the entire thread so this may already have been said.

If a vehicle is travelling directly downwind at the speed of the wind then the vehicle is effectively in a calm and is not in a wind at all. To then travel faster than the wind the vehicle would have to get energy from a calm (no wind) and effectively move against a headwind. Not going to happen anytime soon.

There is a big difference between moving directly with a wind and moving at an angle to a wind (tacking). When a thing accelerates with a wind the wind speed effectively slows. When a thing accelerates at an angle to a wind the wind speed remains constant.

To travel faster than the speed of a wind you have to tack against the wind, not with it. The angle of the blades aren’t tacking against the wind when the blades are moving with directly the wind.

ETA -
A vehicle that could travel directly in the direction of a wind faster that the speed of the wind is a vehicle that could accelerate from a perfect calm in to it’s own headwind.

That's sort of how I looked at it when I joined this thread, but I've had to change my mind since.

Just a couple of points so you don't end up stuck with the same misunderstandings I had at the start...

The wind isn't directly turning the propeller. (If it did, the whole thing would go backwards.)

It's the spinning of the propeller which is pushing the cart forwards, like the fan on the back of a hovercraft.

It's the turning of the wheels (as the cart passes over the ground) which powers the propeller.

Of course, you can't get out any more energy out of the wheels than the amount of (kinetic) energy used-up in the process, slowing down the cart.

It seems obvious that trying to propel the cart forwards using this energy would result in a net loss of velocity (power out < power in).

The clever bit is that they're gearing-down the propeller to produce a greater force with the same (or less) energy.

Unfortunately, gearing-down comes with a cost: Speed.
Normally, pushing the air out behind a craft at a lower speed than the craft is traveling would slow the craft down.

But this is where the wind comes in.

It may be pushing out the air behind it at a slower speed than the craft is moving relative to the ground, but the air isn't pushing against the ground, so the relative speed of the ground is irrelevant. What is relevant is the relative speed of the air.

Since the craft is pushing the air out behind it with a greater force than applied to the wheels, at a speed greater than its traveling through the air, it's speed increases.

It's doing this by exploiting the relative difference between ground and air speeds.


One of the main points of contention with Humber is that he thinks that a vehicle on a treadmill in still air is not equivalent to a vehicle traveling down the road at wind speed.

 

[ynot]

The really astonishing thing, is that they believe (it appears to be belief) that this treadmill is the equivalent of a windtunnel.
A car on a similar belt, with a belt speed of 60mph, IS traveling at 60mph

A “stationary” car on a belt moving at 60mph is equivalent to a car travelling along a road at 60mph with a 60mph tailwind.

 

[sol invictus]

No, but it is taking a good beating

That's right - you, humber, are proving relativity wrong. Apparently the way to do that is to repeat nonsense over and over many times.

A “stationary” car on a belt moving at 60mph is equivalent to a car travelling along a road at 60mph with a 60mph tailwind.

That's precisely what humber refuses to accept. Because once he does this is over - both the videos and a simple force balance analysis show that the cart on the treadmill accelerates against the belt - i.e. it goes downwind faster than the wind. Of course the videos taken outside prove it as well, but it's easier for humber to squirm and complain that the wind wasn't steady, there were bumps, etc.

 

[jsfisher]

Under humberian mechanics, where wind speed (relative to the Earth) is all that matters, a sail boat in a river flowing at 10 MPH would have no trouble maneuvering in a 10 MPH wind. (River flow and wind in the same direction, of course.)

 

[ynot]

That's sort of how I looked at it when I joined this thread, but I've had to change my mind since.

Just a couple of points so you don't end up stuck with the same misunderstandings I had at the start...

The wind isn't directly turning the propeller. (If it did, the whole thing would go backwards.)

It's the spinning of the propeller which is pushing the cart forwards, like the fan on the back of a hovercraft.

It's the turning of the wheels (as the cart passes over the ground) which powers the propeller.

Of course, you can't get out any more energy out of the wheels than the amount of (kinetic) energy used-up in the process, slowing down the cart.

It seems obvious that trying to propel the cart forwards using this energy would result in a net loss of velocity (power out < power in).

The clever bit is that they're gearing-down the propeller to produce a greater force with the same (or less) energy.

Unfortunately, gearing-down comes with a cost: Speed.
Normally, pushing the air out behind a craft at a lower speed than the craft is traveling would slow the craft down.

But this is where the wind comes in.

It may be pushing out the air behind it at a slower speed than the craft is moving relative to the ground, but the air isn't pushing against the ground, so the relative speed of the ground is irrelevant. What is relevant is the relative speed of the air.

Since the craft is pushing the air out behind it with a greater force than applied to the wheels, at a speed greater than its traveling through the air, it's speed increases.

It's doing this by exploiting the relative difference between ground and air speeds.


One of the main points of contention with Humber is that he thinks that a vehicle on a treadmill in still air is not equivalent to a vehicle traveling down the road at wind speed.

A vehicle on a treadmill in still air is NOT equivalent to a vehicle travelling down the road at wind speed when we are talking about whether a vehicle can travel directly downwind faster than the wind.

In the vehicle travelling down the road in the direction of the wind scenario the wind IS directly turning the propeller which then turns the wheels to give forward motion. This cart is not pushing air out behind it.

In the vehicle on the treadmill scenario the treadmill turns the wheels which then turns the propeller to push wind out behind it to gain forward motion.

If you think that the motion of the vehicle along the surface of the road is the thing providing the energy to the propeller to create a backwards wind, where does this energy come from if not the propeller?

Reminds me of a cartoon I’ve seen of a vehicle where the motion of the vehicle turns a fan that blows wind in to a sail to propel it forward.

 

[sol invictus]

I agree with Humber - A vehicle on a treadmill in still air is NOT equivalent to a vehicle travelling down the road at wind speed.

A “stationary” car on a belt moving at 60mph is equivalent to a car travelling along a road at 60mph with a 60mph tailwind.

Huh....

In the vehicle travelling down the road in the direction of the wind scenario the wind IS directly turning the propeller which then turns the wheels to give forward motion.

If the vehicle is moving at the speed of the wind, the air is not moving with respect to it. So exactly how does the wind manage to turn the propeller?

If you think that the motion of the vehicle along the surface of the road is the thing providing the energy to the propeller, where does this energy come from if not the propeller?

It comes from the relative motion of the air and the ground. Once again, the fact that ice boats can sail downwind much faster than the wind proves conclusively that there is no issue with conservation of energy. Any time there is relative motion you can extract energy from it. If you can extract energy you can use it to accelerate, regardless of your current velocity.

 

[Brian-M]

Brian-M,
What will happen if you are a walker in a corridor full of people passing by at a greater speed?

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?

And the difference being that the car on the floor next to the belt, does not have a belt spinning its wheels.
Stop the belt. They are the same. Must be. The wind that wasn't there has gone too.

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.

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.

Because you think there is a difference between one wall and the other, throwing the house at the ball is "exactly" the same?

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.

Now, you can't mean that. Not literally. I know you don't think that you can actually compare a house being thrown at a ball like that....But a car standing still can still be going 60mph

Yes, I can, and I do. It's called relative velocity.

A car standing still can still be going 60 mph relative to something else.

 

[humber]

OK, I'm tired of arguing. You're wrong, you're contradicting every physics book, wikipedia, the collective knowledge of nearly all other posters in this thread, logic, and the evidence of your eyes. On top of that you refuse to put your money where your mouth is.
There's a word for people like you - it's "troll".

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.
Additionally, the car on the treadmill is exactly the same as if it were traveling in a 60mph tailwind, but the car on the floor, not.

 

[jsfisher]

In the vehicle travelling down the road in the direction of the wind scenario the wind IS directly turning the propeller which then turns the wheels to give forward motion. This cart is not pushing air out behind it.

...except the propeller is geared to turn the wheels the other way.

 

[ynot]

Total nonsense. A long while back modified gave an example of a device that sails directly downwind faster than the wind (two iceboats jibing back and forth connected by a bar). More simply, it's trivial to travel at an angle downwind much faster than the wind - and I mean with your speed in the wind direction faster than the wind, not just your total speed.

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

 

[Brian-M]

A vehicle on a treadmill in still air is NOT equivalent to a vehicle travelling down the road at wind speed when we are talking about whether a vehicle can travel directly downwind faster than the wind.

In the vehicle travelling down the road in the direction of the wind scenario the wind IS directly turning the propeller which then turns the wheels to give forward motion. This cart is not pushing air out behind it.

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?

If you think that the motion of the vehicle along the surface of the road is the thing providing the energy to the propeller to create a backwards wind, where does this energy come from if not the propeller?

In both cases, the ground passing under the wheels.