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Down wind faster than the wind

mhaze said:
By the way in this thread I have not seen an aerodynamic approach to the issues at all. Here I am referring to the conceptual frameworks and grammer as used in such a discussion, as opposed to physics and vectors. Humber comes close with his noting that air close to the cart on the treadmill is stationary, and this is not the same as airflow in the open field.
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Et tu, Brute?

I'm truly shocked by the lack of even rudimentary physics knowledge displayed here, especially by self-styled engineers.

Here's an analysis of the forces, since so many of you seem incapable of doing it yourself.

Use the frame in which the cart is stationary, the air is stationary, the ground is moving, and the wheels are spinning. That frame and initial condition are physically identical in every way to a situation in which the cart starts off rolling along the ground at exactly the speed of a steady wind. We'll ignore friction, air resistance other than what is relevant to the propeller, and assume the wheels and connection from wheels to propeller can't slip. We want to know if the cart can go faster than the wind, which would mean it accelerates from this initial condition in a direction such that it increases its speed relative to the ground (and its wheels spin faster).

The physics is simple. If the wheels weren't connected to the propeller, Newton's first tells us the cart would remain stationary in this frame (no friction, and no wind force on the propeller since the air is still). When the wheels are connected the propeller spins and generates a force. There is also a force from the torque on the wheels (which is now non-zero since there is resistance from the propeller).

To see what happens next, consider re-orienting the propeller. If you aim it up, like a helicopter, there will be a force up from that, and a force back from the wheels, so the cart will start to fall back (i.e. move with the ground, with its wheels spinning slower). If you orient it so it pushes back, the cart will fall back faster. But if you orient it so it pushes forward, opposite to the ground motion, there are two forces acting in opposite directions and one must check their magnitudes. There is no principle which says one must be bigger than the other - and given some assumptions about the propeller and the gearing one could easily estimate them. If the propeller force is larger, the cart will move forward against the direction of the ground motion - which means faster than the wind.

I have not done the estimate of the forces, which is why (as I have said all along) I don't consider it obvious that this particular design will work. However there is no reason why it shouldn't, and the videos are convincing. The burden of proof is fully on anyone that doubts it - there is no legitimate reason given by anyone here why it shouldn't work.
That's it.
 
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sol invictus said:
Et tu, Brute?

I'm truly shocked by the lack of even rudimentary physics knowledge displayed here, especially by self-styled engineers.

Here's an analysis of the forces, since so many of you seem incapable of doing it yourself.

Use the frame in which the cart is stationary, the air is stationary, the ground is moving, and the wheels are spinning. That frame and initial condition are physics identical in every way to a situation in which the cart is rolling at exactly the speed of a stead wind. We'll ignore friction, air resistance other than what is relevant to the propeller, and assume the wheels and connection from wheels to propeller can't slip. We want to know if the cart can go faster than the wind, which means it accelerates from this initial condition in a direction such that it increases its speed relative to the ground (the wheels spin faster).

The physics is simple. If the wheels weren't attached, Mr. Newton tells us the cart would remain stationary in this frame (no friction and no wind force on the propeller since the air is still). When the wheels are connected the propeller spins and generates a force. There is also a force from the torque on the wheels (which is now non-zero since there is resistance from the propeller).

To see what happens next, consider re-orienting the propeller. If you aim it up, like a helicopter, there will be a force up from that, and a force back from the wheels, so the cart will start to fall back (i.e. move with the treadmill). If you orient it so it pushes back, the cart will fall back faster. But if you orient it so it pushes forward, opposite to the treadmill motion, there are two forces acting in opposite directions and one must check their magnitudes. There is no principle which says one must be bigger than the other - and given some assumptions about the propeller and the gearing one could easily estimate them. If the propeller force is larger, the cart will move forward against the direction of the treadmill motion - which means faster than the wind.

I have not done this estimate, which is why (as I have said all along) I don't consider it obvious that this particular design will work. However there is no reason why it shouldn't, and the videos are convincing. The burden of proof is fully on anyone that doubts it - there is no legitimate reason given by anyone here why it shouldn't work.
That's it.
Click to expand...

And I get to take yet another breath of very fresh air.

Thanks sol.

JB
 
sol invictus said:
No. Read it again.

Again, I have no idea what you're talking about. You evidently have some scenario in your head you haven't told the rest of us about, which makes it hard to understand you.
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No. There is no wind blowing over the cart at any time. The car held in the hand is the same as said to be at windspeed. The incremental gain that you see, is the actual speed relative to ground.

Your model is wrong, because, as has been stated several times, the belt is the wind, but it is not it is the ground. Otherwise the porpeller should be embedded in the belt. This is not a new frame of reference.

The cart is the cart
The wheels are the wheels
The belt is the ground ( connected to the real ground of the treadmill body)
The air is the air
The propellor is the propellor
The observed speed is the actual speed relative to ground

Is it not amazing that this light cart is not blown away by the wind. Seems to happen in the video.
There is no wind. The concept is a sophism.

Please note that this thread has a high Einstein citation index.
 
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humber said:
No. There is no wind blowing over the cart at any time.
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This is amazing.

How much education in physics do you have? Have you taken the equivalent of a first-year college course?

Your model is wrong, because, as has been stated several times, the belt is the wind, but it is not it is the ground. Otherwise the porpeller should be embedded in the belt.
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"the belt is the wind, but it is not it is the ground. Otherwise the porpeller should be embedded in the belt."

Are you a random text generator?
 
humber said:
No. There is no wind blowing over the cart at any time. The car held in the hand is the same as said to be at windspeed. The incremental gain that you see, is the actual speed relative to ground.

Your model is wrong, because, as has been stated several times, the belt is the wind, but it is not it is the ground. Otherwise the porpeller should be embedded in the belt. This is not a new frame of reference.

The cart is the cart
The wheels are the wheels
The belt is the ground ( connected to the real ground of the treadmill body)
The air is the air
The propellor is the propellor
The observed speed is the actual speed relative to ground

Is it not amazing that this light cart is not blown away by the wind. Seems to happen in the video.
There is no wind. The concept is a sophism.

Please note that this thread has a high Einstein citation index.
Click to expand...

And how can an observer sitting on the cart tell if the ground (treadmill) is moving under the cart with no wind, or the cart is moving with the wind over a stationary ground (treadmill)?
 
Yes. Simple arithmetic calculations. Why bother with the real windspeed over the cart, when you can simply eliminate it by subtracting the belt speed.
 
humber said:
Yes. Simple arithmetic calculations. Why bother with the real windspeed over the cart, when you can simply eliminate it by subtracting the belt speed.
Click to expand...

FINALLY!!! (if only you weren't being sarcastic)
 
humber said:
Yes. Simple arithmetic calculations. Why bother with the real windspeed over the cart, when you can simply eliminate it by subtracting the belt speed.
Click to expand...

Is your claim that the cart can never get up to windspeed in the first place?
 
sol invictus said:
The physics is simple. If the wheels weren't connected to the propeller, Newton's first tells us the cart would remain stationary in this frame (no friction, and no wind force on the propeller since the air is still). When the wheels are connected the propeller spins and generates a force. There is also a force from the torque on the wheels (which is now non-zero since there is resistance from the propeller).
Click to expand...
The physics is simple and yet you think there is zero torque on a cart rolling on a treadmill? :hb:
 
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On the belt, the cart is at windspeed, with a little forward motion.
Stop the belt and the cart will remain in place.
That difference in velocities is the actual difference between the cart's velocity in the presence of wind and still air.

Conclusion.This is not a model of the real cart in wind.
 
technoextreme said:
The physics is simple and yet you think there is zero torque on a cart rolling on a treadmill?

<snip>
Click to expand...

Huh? Sol explicitly stated that by connecting the propeller to the wheels means a torque greater than zero is required to turn the wheels. With suitable gearing and propeller selection the net force from the treadmill on the cart and the prop can be adjusted (in theory and apparently in practice) to be in a direction which causes the cart to accelerate to above the speed of the treadmill.
 
It's not a claim, because the concept is nonsense. To try to answer your question, the cart is assumed to be at windspeed when placed upon the belt.

Ignoring the observed tiny speed. we have two options:
The cart is at windspeed when in the hand or on the belt. ( no sensible wind over cart)
The cart is at zero velocity when in the hand or on the belt. ( no sensible wind over cart)
It's paradoxical, because it is nonsense.
This platform represents a cart that keeps itself at zero velocity regardless of windspeed.
It is understandable, but unbelievable that such a model would be proposed. That's the difficulty of understanding.
All this headbanging is astonishment at support of such a banal and absurd claim. It is not even wrong.
 
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Ivor the Engineer said:
Huh? Sol explicitly stated that by connecting the propeller to the wheels means a torque greater than zero is required to turn the wheels.
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Which is wrong from a physics standpoint. You always need a torque greater than zero to turn a wheel.
With suitable gearing and propeller selection the net force from the treadmill on the cart and the prop can be adjusted (in theory and apparently in practice) to be in a direction which causes the cart to accelerate to above the speed of the treadmill.
Click to expand...
Right but it needs to be done in BOTH DIRECTIONS at the same time in order to travel faster than wind. You can't do it with just a belt drive.
 
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I have to wonder - if Galileo, Newton, and Einstein came back from the dead to explain this in simple terms, mathematical formulas, and simple pictures (using multiple colored markers) - would humber and techno tell them they're all idiots?

I take it back. Of course they would.
 
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ivor:
Huh? Sol explicitly stated that by connecting the propeller to the wheels means a torque greater than zero is required to turn the wheels.
Click to expand...
-
techno:
Which is wrong.
Click to expand...

How can it be wrong techno? With the propellor attached, a torque greater than zero IS required to turn the wheels.

First you incorrectly say Sol thinks it's zero. When it's pointed out to you that So correctly said "non-zero" you now say it's wrong.

So, we have a clearly stated position from techno:

It's insane to think the torque is zero and it's wrong to think it's non-zero.

I rest my case.

JB
 
spork said:
I have to wonder - if Galileo, Newton, and Einstein came back from the dead to explain this in simple terms, mathematical formulas, and simple pictures (using multiple colored markers) - would humber tell them they're all idiots?
Click to expand...

There's no need to wonder.

JB
 
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