Merged DDWFTTW in a “Real” Wind

[Modified]

Already answered. If you want to talk about a brick on a treadmill I find that very uninteresting.

But if you don't even understand a brick on the treadmill, how can you hope to understand the cart? A brick on the treadmill belt must be compared to a brick on the road in a wind the same speed as the treadmill belt. In both cases, the experience of the brick is the same. A cart moving at air speed on the treadmill belt must be compared to a cart moving at airspeed on the road.

 

[Modified]

You can say wrong all you like, but it is you who is wrong.

In what way? You are comparing in one case air movement relative to a surface with in another case air movement relative to something else (a room that is moving relative to the surface). You can call them both "wind" if you like, but you are using two different meanings of "wind".

 

[Jack by the hedge]

Not true at all. The wind on the treadmill is relative to the motion of the objects on the tread moving through still air. Different objects will move at different velocities and have different winds. Your premise is wrong. It is not the same for ALL.

Already answered. If you want to talk about a brick on a treadmill I find that very uninteresting.

When you say "already answered", I gather that you agree it is trivially true that an anemometer fixed to the treadmill rolling backwards at 10mph would register the same 10mph windspeed as the same anemometer on the ground with a 10mph wind blowing over it.

From your point of view, it appears, "wind" is not the speed of the air relative to the ground but rather the speed of the air relative to the cart.

Using your definition of "wind" if you like, can you point out any dissimilarity between a cart travelling at 10mph over the ground in air which is also travelling at 10mph and a cart remaining in place in still air while a belt travels backwards at 10mph beneath it?

 

[Jack by the hedge]

On the surface of the earth it is that friction which dominates over the inertial mass, to keep the object in place. If you want to move that object along the surface you must break the bond of static friction and then keep working against the kinetic friction whether rolling or sliding. The role of inertia is masked by that friction in normal non-laboratory settings. That is what I am talking about here, normal setting with a cart on a road, energy must be used to move against mgk where k is the coefficient of friction. Only if the object is on a frictionless surface can inertia play a significant role.

Wheels are often useful in this regard. A fully laden trolley is hard to get going, but once it's moving it's almost as easy to keep going as an empty one. That's inertia, being significant, out of the lab.

Ah, but we have seen that the treadmill can cause the cart to move up the belt in still air. Spork has already agreed the energy to do that is coming from the treadmill and not the wind...

The misinterpretation here has already been dealt with but the fundamental problem is a failure to accomodate different frames of reference. Kinetic energy is frame dependent. Who provides energy to whom is frame dependent. Rejection of the equivalence of inertial frames of reference will make this simple stuff almost impossible to understand. Trying to run before you can walk is a recipe for falling flat on your face.

I know a lot of qualified people and I have already asked. Contrary to what you say, I have found no qualified physicist who believes the treadmill is the same as a road.

It seems likely to me that what you asked them was not exactly what you imagine you asked them, or you misunderstood their answers. That is enormously more likely than the possibility of your knowing a large number of qualified physicists who do not accept the equivalence of inertial frames of reference.

 

[69dodge]

The wheels spin and that makes the propeller spin creating thrust. The thrust is the horizontal force that keeps the cart from moving back with the tread.

Yes, I agree.

So, a cart with spinning wheels, and therefore with a spinning propeller, can resist the backward force of the tread on its wheels.

In fact, it is the very backward force on its wheels which causes the wheels, and therefore the propeller, to spin, providing enough thrust not only to keep the cart from moving backward but actually to move it forward.

All of the power comes from the treadmill through the wheels. This is not a wind powered cart in any sense at all. It has no relation to a cart on the road that is wind powered.

What if you were standing on the treadmill (not walking)? How would things look to you?

You'd see the tread as stationary. You'd feel the air moving forward. You'd see the cart next to you moving forward faster than the air, even though the treadmill is pushing backward on the cart (or, rather, because the treadmill is pushing backward on it).

I see a close relation between that situation and one where you're standing on the ground in a wind, with the cart moving past you faster than the wind, even though the ground is pushing backward on the cart (or, rather, because the ground is pushing backward on it).

 

[quarky]

How about a new metaphor?

A person falls down a flight of stairs. Boom, kaboom, clunk, bang, thunk, ouch. Rest.
(gravity heavily involved.)

A person falls down an escalator that is going up: Boom, clang, bump, thunk, ouch, etc...except it goes on and on; he never stops falling; never makes it to the bottom of the stairs.

 

[69dodge]

Would the air be doing work on the cart if the propeller were not turning?

No. In that case, the cart would be doing work on the air.

It seems the cart must do work on the air in order for the air to have any effect on the cart.

Why? If the air does work on the cart, that would also result in the air having an effect on the cart.

And [...] it must travel over the ground, turning its wheels against the friction of the ground, so it is doing work on the ground. It is also pushing into its relative headwind doing work on the air ahead of it.

Right. Or, at least, the parts of it other than the propeller are pushing into the relative headwind. The propeller, because of its shape and because it's spinning, is essentially in a tailwind.

It is doing a lot of work for something that has no energy source!

But it has an energy source: the difference in speed between the air and ground.

 

[69dodge]

How about a new metaphor?

A person falls down a flight of stairs. Boom, kaboom, clunk, bang, thunk, ouch. Rest.
(gravity heavily involved.)

A person falls down an escalator that is going up: Boom, clang, bump, thunk, ouch, etc...except it goes on and on; he never stops falling; never makes it to the bottom of the stairs.

Ouch.

But what is it a metaphor for?

 

[humber]

Why doesn't the backward-moving treadmill belt cause the cart to move backward with it, instead of causing its wheels to spin? (It would cause you to move backward if you were standing on it.)

But, it wouldn't if you had wheels. It would take little force to prevent motion down the belt if you were wearing roller skates. A small restraining force to a handrail would do the trick, as the wheels spun and you stayed in place.

You could no more said to be "traveling", than a person on the floor, who's restraining force was friction to the ground.

The prop provides that small force. "Climbing of the belt" is simply a false assertion.
The wheels act as an idler, a transmission, between the prop and the belt, which is itself, a transmission to the motor. It is nothing more than a toy driven by a motor in still air.

What if you were standing on the treadmill (not walking)? How would things look to you?

And how would the belt drive the feet to produce walking? It seems the "transform" works only for wheels.

 

[humber]

How about a new metaphor?

A person falls down a flight of stairs. Boom, kaboom, clunk, bang, thunk, ouch. Rest.
(gravity heavily involved.)

A person falls down an escalator that is going up: Boom, clang, bump, thunk, ouch, etc...except it goes on and on; he never stops falling; never makes it to the bottom of the stairs.

Yes. How about the person "curls up" and spins in place?

 

[Jack by the hedge]

What if you were standing on the treadmill (not walking)? How would things look to you?

And how would the belt drive the feet to produce walking? It seems the "transform" works only for wheels.

What are you talking about? Standing on a treadmill and not walking does not require the treadmill to "produce walking". The transform (from the ground's point of view to the air's point of view) works perfectly well, thanks. Neither the air nor the ground "produce walking".

 

[quarky]

Ouch.

But what is it a metaphor for?

The irrelevance of gravity's role in this.

 

[humber]

What are you talking about? Standing on a treadmill and not walking does not require the treadmill to "produce walking". The transform (from the ground's point of view to the air's point of view) works perfectly well, thanks. Neither the air nor the ground "produce walking".

Oh, but it does. The walker has to provide the power to walk. The belt can't do that. Why should a wheeled object be any different?
Galilean Transforms demand mechanical equivalence, and that has not been met. This is largely a waste of time, because the TM has been dismissed by Spork's selected expert, and because of carts that work without a prop.

 

[Jack by the hedge]

Oh, but it does. The walker has to provide the power to walk. The belt can't do that. Why should a wheeled object be any different?
Galilean Transforms demand mechanical equivalence, and that has not been met.

Stop. Think. Why does standing on a treadmill and not walking require the treadmill to "produce walking"?

 

[Jack by the hedge]

If, on the other hand, the person is walking, then whether they're on the ground or on a treadmill they must produce the walking. Equivalence.

Why should a wheeled object be different? It isn't.

 

[ThinAirDesigns]

Christoph/ChrisopherMa/Harold/Schroeder/Yevgheni/profpangloss arguments are only the equal of chasing tails. He will not stick to consistent positions. This is typical.

For two years now we've seen his argument and they are unchanged -- he simply can't follow relative motion.

The argument 'the ground can't power anything' changes to something else when it's shown that a simple wind turbine is ALWAYS powered by the ground in the frame of the wind -- the argument must change so he changes it.

He claims that a treadmill can't create wind and then ducks the obvious -- that any anemometer in the world will register the same speed as the threadmill if placed on the belt.

Same old flawed arguments and he won't convince a soul precisely because of those flaws.

JB

 

[3point14]

"it's telling" is a hackneyed rhetorical device, frequently employed to suggest superior knowledge or insight. It so often fails.

I didn't know you did literary criticism. Are you an expert in that too?

 

[humber]

Christoph/ChrisopherMa/Harold/Schroeder/Yevgheni/profpangloss arguments are only the equal of chasing tails. He will not stick to consistent positions. This is typical.

For two years now we've seen his argument and they are unchanged -- he simply can't follow relative motion.

The argument 'the ground can't power anything' changes to something else when it's shown that a simple wind turbine is ALWAYS powered by the ground in the frame of the wind -- the argument much change so he does.

No such argument exists. The wind powers a wind turbine not the ground.
There is no engineer that will tell you otherwise.

Once again more evidence that a cranky power generation scheme is underway. This one will be stillborn.

He claims that a treadmill can't create wind and then ducks the obvious -- that any anemometer in the world will register the same speed as the threadmill if placed on the belt.

Actually, it won't, but that relates to what will be given to NALSA, so you will have to wait.

 

[humber]

I didn't know you did literary criticism. Are you an expert in that too?

And you assume significant expertise is necessary to finding fault with Carteerian diatribes?

 

[Jack by the hedge]

Actually, it won't, but that relates to what will be given to NALSA, so you will have to wait.

Any hint of how long?