Down wind faster than the wind

[spork]

Show of hands... does ANYONE here fail to see the irony of the "thinker" tag below humbers name?

 

[humber]

Show of hands... does ANYONE here fail to see the irony of the "thinker" tag below humbers name?

Ditto "scholar", but then again, that's no answer is it?

 

[Cuddles]

This rather reminds me of the "NIST invented thermal expansion" nonsense from various conspiracy theorists.

 

[humber]

This rather reminds me of the "NIST invented thermal expansion" nonsense from various conspiracy theorists.

I have to agree, but this is more than that. This is not a "plane on a treadmill argument" but a claim for a real device, that is being promoted here, other websites, and You Tube. If "stop Sylvia Browne" is a suitable thread, the so is "stop pseudo-scientific nonsense".

 

[Ivor the Engineer]

Ivor,
Yes. All bodies within the braked vehicle will react to the loss of kinetic energy. They will therefore "slowdown" which is felt as forward or backward motion ( dependent upon arbitrary choice as to which is forward. )

You have not responded to my remark concerning the wind.

I wanted to confirm you accept all motion is relative.

Put the treadmill in a vehicle. Drive downwind at windspeed. Open the window and put the toy outside. Now what happens?

<snip>

While in the car on the treadmill, the toy travels faster than the car, getting energy from the difference in speed between the "still" air and the "moving" treadmill.

When placed on the ground, the toy overtakes and pulls away from the car, getting energy from the difference in speed between the "still" ground and "moving" air.

 

[spork]

This rather reminds me of the "NIST invented thermal expansion" nonsense from various conspiracy theorists.

Not familiar with it. Care to share?

 

[CyCrow]

Ivor,
Yes. All bodies within the braked vehicle will react to the loss of kinetic energy. They will therefore "slowdown" which is felt as forward or backward motion ( dependent upon arbitrary choice as to which is forward. )

Actually, they will not "react to the loss of kinetic energy". The braking vehicle is accelerating, and is therefore NOT an intertial reference system. The reference system cannot be attached to the vehicle, it must have constant velocity.

You have not responded to my remark concerning the wind.

Put the treadmill in a vehicle. Drive downwind at windspeed. Open the window and put the toy outside. Now what happens?
Is seems that some would have you equate "inertial frames of reference" with "point of view". You have to travel with the treadmill (simulator) in each case!

What happens? Same as on the treadmill in still air. When driving downwind at windspeed, relative air motion is zero. We have been trying to tell you this. It doesn't make a difference at this point if the vehicle is on a treadmill moving at ground speed, or on the ground.

No, your argument is not Galilean, but based upon pre-scientific notions. If this "treadmill system" could be idealized, the vehicle, when placed on the ground, would be immovable in the given direction.
The drag and motive forces, of any magnitude, would always oppose each other so as to prevent motion. This is clearly impossible to realise in practice. The treadmill is an imperfect model of that situation. Nothing more.

Are you confusing the constant speed treadmill in this experiment with the idealised treadmill in the "plane on a treadmill" case? The one that could accelerate instantly and indefinetely to try to keep the plane from taking off? If so, hey you have a chance to understand your misunderstanding.

The real cart does move with the wind, but that is because its real model is not that of the treadmill. In the latter case, the "treadmill" is not part of "the system" but part of the vehicle itself.

ETA:
To anticipate an escape route. If this device exploits a putative "propeller tip effect", then this must apply to all existing propellers. Such effects have not been observed.

I'm not sure what kind of "tip effect" you are alluding to, but in general aerodynamic tip effects reduce the performance of propellers, and as such are not used to support the analysis. However, the fact that the propeller tips are moving through the air at a higher rate than the vehicle ground speed is exploited to generate lift/thrust.

// CyCrow

 

[Cuddles]

Not familiar with it. Care to share?

One of the recent claims by some 9/11 conspiracy nuts is that NIST (the engineering body who produced the report into the collapse of the World Trade Center towers) invented the non-existent concept of thermal expansion in order to get their collapse models to work. It's rather odd in that the idea of things expanding when they get hot is really amazingly basic physics that most people have observed themselves without even needing to be taught about it. I find Humber's constant dismissal of the similarly basic concept of relative velocities and energies, despite having it explained repeatedly by several people, rather similar.

I have to agree, but this is more than that. This is not a "plane on a treadmill argument" but a claim for a real device, that is being promoted here, other websites, and You Tube. If "stop Sylvia Browne" is a suitable thread, the so is "stop pseudo-scientific nonsense".

I don't think you quite understood my point. You are the one claiming that people are making up imaginary concepts when they try explaining basic physics to you.

 

[CyCrow]

Appearances can be deceptive, don't you think?

The auto-gyro will obey Newton's laws in each case. Without drag, it falls faster.
Gravity pulls on the autogyro. The air passing over the propeller, turns it. In principle, this drag is is no different from that of a parachute

It's clear you don't understand the autogyro. Assuming you are alluding to a traditional round parachute, not the modern square airfoil-shaped ones, there is a very important difference. Lift. It's what enables autogyros (and airplanes) to fly with much less thrust than weight. Propellers, being rotating airfoils, also generate lift at a much higher rate than drag. That's the key to going downwind faster than the wind.

// CyCrow

 

[sol invictus]

No, your argument is not Galilean, but based upon pre-scientific notions. If this "treadmill system" could be idealized, the vehicle, when placed on the ground, would be immovable in the given direction.

Huh? What in the world are you talking about?

The drag and motive forces, of any magnitude, would always oppose each other so as to prevent motion.

Gibberish. It does sound like you have some warped version of the plane on a treadmill story in mind, but it's really boring trying to guess what it is. This treadmill moves at constant speed because we want it to be equivalent to a constant wind speed.

This is clearly impossible to realise in practice. The treadmill is an imperfect model of that situation. Nothing more.

The real cart does move with the wind, but that is because its real model is not that of the treadmill. In the latter case, the "treadmill" is not part of "the system" but part of the vehicle itself.

No, actually the cart outside in the wind behaves precisely like the one inside on the treadmill (apart from variations in wind speed and bumps in the path). Just as is guaranteed by the fundamental principles of physics.

ETA:
To anticipate an escape route. If this device exploits a putative "propeller tip effect", then this must apply to all existing propellers. Such effects have not been observed.

I have no idea what you mean. You're so confused about this your anticipated "escape routes" are incomprehensible to anyone but you.

 

[humber]

Actually, they will not "react to the loss of kinetic energy". The braking vehicle is accelerating, and is therefore NOT an intertial reference system. The reference system cannot be attached to the vehicle, it must have constant velocicty.
[\QUOTE]

What happens? Same as on the treadmill in still air. When driving downwind at windspeed, relative air motion is zero. We have been trying to tell you this. It doesn't make a difference at this point if the vehicle is on a treadmill moving at ground speed, or on the ground.

Are you confusing the constant speed treadmill in this experiment with the idealised treadmill in the "plane on a treadmill" case? The one that could accelerate instantly and indefinetely to try to keep the plane from taking off? If so, hey you have a chance to understand your misunderstanding.

I'm not sure what kind of "tip effect" you are alluding to, but in general aerodynamic tip effects reduce the performance of propellers, and as such are not used to support the analysis. However, the fact that the propeller tips are moving through the air at a higher rate than the vehicle ground speed is exploited to generate lift/thrust.

// CyCrow

The braking vehicle is accelerating, but negatively. This is why I put "slowing down" within quotes. Most assume acceleration to only be "positive".
One represents the loss of kinetic energy, the other an increase.

A differential veloivity of zero, does not mean no drag. If fact, I can demonstrate this using your own "frames" idea.
Hold the vehicle within a tailwind. There is drag, as the wind flows over the static vehicle. Put that in a mental "van". Add say, 10mph, downwind to that. Add up the vectors. What do you get? The same drag as when static.

The "tip effect" is not of my doing, but an explanation given to support the idea that the vehicle in some way acts as if it were tacking the wind.

You are indeed confusing "inertial frames" with the observer's view.
At a stretch, the device may be though of as being in a separate inertial frame while accelerating, but no at any other time. The velocities are too low to even consider any other effects such as time dilation or mass increase.

Lift and so forth have nothing to do with the treadmill.

 

[humber]

I don't think you quite understood my point. You are the one claiming that people are making up imaginary concepts when they try explaining basic physics to you.

Well I did not take your point, but you did mine. Quite obviously, I am claiming that they have made up concepts that are not only imaginary, but contradict their own claims, so it both contradicts the known laws, but is also internally inconsistent.
The device on the treadmill is not the craft. It is a model of the effect of Newton's law of action and reaction. Thus these same laws are used in support, and refutation.

 

[Modified]

Can you show me a wind-driven prop that does not "extract energy from the difference between the wind and the ground"

Yes, a windmill extracts energy from the difference between the speed of the wind and the windmill base. The speed of the ground is irrelevant, though many windmills are fixed to the ground.

 

[Ivor the Engineer]

<snip>

A differential veloivity of zero, does not mean no drag.

<snip>

 

[humber]

Huh? What in the world are you talking about?

Gibberish. It does sound like you have some warped version of the plane on a treadmill story in mind, but it's really boring trying to guess what it is. This treadmill moves at constant speed because we want it to be equivalent to a constant wind speed.

No, actually the cart outside in the wind behaves precisely like the one inside on the treadmill (apart from variations in wind speed and bumps in the path). Just as is guaranteed by the fundamental principles of physics.

I have no idea what you mean. You're so confused about this your anticipated "escape routes" are incomprehensible to anyone but you.

No, the forces of drag created by the prop, equal the drive, to produce zero velocity. If idealised, that would apply to the real vehicle. It could not move.

The real vehicle has a drag that is proportional to the velocity. At low speeds it is low, but as the velocity rises, so does the drag. When the drag equals the drive,that is the terminal velocity of the device.

If you still think the treadmill represents performance at windspeed, drive at windspeed, release it, and see what happens. It will not run along side as suggested.
In the van model turn the treadmill around. It fails to react. Turn off the drive motor, no visible difference (though prop no longer turns)
Stop the van, reverse the van, go beyond windspeed. The treadmill provides exactly the same information in all cases.
At least 9/11 claims have some air of plausibility.

 

[humber]

Yes, a windmill extracts energy from the difference between the speed of the wind and the windmill base. The speed of the ground is irrelevant, though many windmills are fixed to the ground.

Energy is extracted from the wind passing over the prop. Indeed, the speed of the ground is irrelevant, but you think it is.

 

[ThinAirDesigns]

George:

At least 9/11 claims have some air of plausibility.

It all makes sense now.

JB

 

[humber]

This is an imaginary scenario. Even if there were no drag at windspeed ( zero differential velocity), then a little slower or a little faster would produce drag.
The treadmill ( though by no means a model), represents this knife-edge, of the balance forces of drag and drive obtained from the belt.

But this is not even a "theoretical" point, because in order to reach it, the craft must first break the drag barrier, requiring over-unity.
The thought experiments are bizarre enough, but they simply gloss over the manner in which the craft might get to this supposed state.

 

[humber]

George:


It all makes sense now.

JB

How so? I make no connection with 9/11. Like the plane on a belt, it is a distraction.

 

[humber]

It's clear you don't understand the autogyro. Assuming you are alluding to a traditional round parachute, not the modern square airfoil-shaped ones, there is a very important difference. Lift. It's what enables autogyros (and airplanes) to fly with much less thrust than weight. Propellers, being rotating airfoils, also generate lift at a much higher rate than drag. That's the key to going downwind faster than the wind.

// CyCrow

The sum of the lift and drag forces are always zero. Specific designs alter the ratio, but not the sum. Low drag items fall faster (a vacuum being the limiting case). Any prop that is driven by an external source such as a motor, is of course a different matter.