Merged DDWFTTW in a “Real” Wind

[ThinAirDesigns]

Spork has already agreed the energy to do that is coming from the treadmill and not the wind.

He has claimed nor agreed to any such thing.

JB

 

[profpangloss]

Profpanglos, you apparently agree that energy is frame dependent. Excellent.

In the frame of the wind before it encounters the blades of a garden variety wind turbine, what (besides the correct answer "ground") powers the wind turbing.

Thanks
Je

Sure you can look at it that way if you want to drive yourself batty. But what is the point? Isn't it much more practical to say the turbine is stationary in the frame where the ground is also stationary and the wind is moving and powering the turbine? Here we are discussinga cart that is claimed to be moving faster than the wind, so in the frame of the wind the cart is moving into still air ahead of it creating a headwind. There will be no tailwind acting on the cart. What are you claiming, the ground is powering the cart? The ground only has relative motion if the cart is moving and it cannot be powering the cart. You are making a joke, right?

 

[profpangloss]

Energy is not an intrinsic property something has. Energy is frame dependent, like velocity. In the frame of the cart (at steady speed), the propeller does in fact put energy into the air. It does this by accelerating the air relative to the cart. In this case the cart gets its energy from the treadmill.

What does this say?

 

[spork]

...the gravitational mass of the object, under the acceleration of gravity is equal to a downward force that the object exerts on the surface of the planet, correct? That force is met by an equal force upwards, the force normal, that the planet exerts on the object. Where the object meets the surface there is friction. 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.

This is the old complaint that somehow gravity manages to hold the cart forward while the treadmill belt spins its wheels. But gravity doesn't hold rolling carts in any horizontal fashion on horizontal surfaces.

 

[ThinAirDesigns]

What does this say?

It's more important what it *does not say*. It does not say "and not from the wind". You claimed that spork agreed that the power was not coming from the wind and that is not the case.

Spork claims (and is correct) that the treadmill is providing the power to *produce* the wind and then that wind (relative motion beween air and surface) is powering the device.

It matters not what is ultimately creating the relative motion between surface and air (the wind), it might be an electric motor attached to a fan (a wind tunnel). It might be an electric motor attached to a belt (treadmill). It might be a nuclear power plant powering a steam turbine spinning a propeller (aircraft carrier). No matter how the wind is produced, all wind powered devices will behave identically.


JB

 

[A.T.]

Indeed. It sounded like an innocent enough question - but the parallels are becoming increasingly obvious.

It is a very characteristic cognitive dissonance: "The ground can have kinetic energy in some frames, but for unexplained reasons it cannot transfer that energy to other objects."

 

[ThinAirDesigns]

Sure you can look at it that way if you want ...

Excellent, you agree that in the frame of the wind, a wind turbine is "ground powered". This is great progress. What this means is that if we planted our wind turbine in the middle of a road running parallel to the wind, we could also just as correctly say that our wind turbine is "powered by the road".

But what is the point?

-

I don’t know of any examples where the road is a source of energy for vehicles travelling on it.

I thought the point would be obvious -- wind powered devices and vehicle (sailboats, land yachts, wind turbines) CAN be powered by the road. You seemed to think that they could not be.

What are you claiming, the ground is powering the cart?

In the frame of the wind, of course the ground is powering the cart.

You are making a joke, right?

You agree that a wind powered turbine can be 'ground powered', but for some reason you assert that a wind powered cart can't. This inconsistency in your position would mean the joke is on you.

JB

 

[ThinAirDesigns]

... the parallels are becoming increasingly obvious.

Without a doubt.

JB

 

[profpangloss]

It's more important what it *does not say*. It does not say "and not from the wind". You claimed that spork agreed that the power was not coming from the wind and that is not the case.

Spork claims (and is correct) that the treadmill is providing the power to *produce* the wind and then that wind (relative motion beween air and surface) is powering the device.

It matters not what is ultimately creating the relative motion between surface and air (the wind), it might be an electric motor attached to a fan (a wind tunnel). It might be an electric motor attached to a belt (treadmill). It might be a nuclear power plant powering a steam turbine spinning a propeller (aircraft carrier). No matter how the wind is produced, all wind powered devices will behave identically.


JB

A treadmill does not produce any significant wind, just some movement at the very surface but it is not like a fan. Hold a paper sail over the moving belt and you can see there is no wind there only still air. What is powering the cart on the treadmill is the belt spinning the wheels. Once the propeller turns it produces a thrust force on the still air, moving it but that is not the source of energy. To use spork's own words, the propeller does in fact put energy into the air.
That doesn't sound like he is saying the cart on the treadmill is a wind powered device! Maybe you and spork should talk it over between yourselves?

 

[humber]

Humber- please explain exactly how a runner on a treadmill in still air experiences any physical differences from a runner on the road with a tailwind.

The runner in the wind, doesn't have a motor, and can take a leak behind a bush. There are countless discussions and technical reports, describing the differences of running of a treadmill and a road.

http://www.answerbag.com/q_view/487519

Not all the answers are correct, but there a sporting "Carteers" too.
Consult established reference for the facts.

ETA: and we are still waiting for you to explain exactly how you can differentiate between the three aircraft carrier scenarios by jumping up and down.

1) It's a JB-ism, so wrong.
2) The Captain will put you in the brig on all three occasions.

 

[temporalillusion]

The "don't check the reference" approach has busted you flat.
Only you think the ship has any relevance, so you may keep it as a blanky if you like.

I'd make an "invisible reference" lolcat pic but it's not worth the effort, so just imagine it.

 

[ThinAirDesigns]

A treadmill does not produce any significant wind, ...

That's odd -- set an anemometer on the belt of a long treadmill and set the treadmill at 10mph. What do you suppose the readout of the anemometer will say?

JB

 

[profpangloss]

Excellent, you agree that in the frame of the wind, a wind turbine is "ground powered". This is great progress. What this means is that if we planted our wind turbine in the middle of a road running parallel to the wind, we could also just as correctly say that our wind turbine is "powered by the road".



-


I thought the point would be obvious -- wind powered devices and vehicle (sailboats, land yachts, wind turbines) CAN be powered by the ground. You seemed to think that they could not be.



In the frame of the wind, of course the ground is powering the cart.



You agree that a wind powered turbine can be 'ground powered', but for some reason you assert that a wind powered cart can't. This inconsistency in your position would mean the joke is on you.

JB

I don't think so. It can be ground powered only up to a point. If it is stationary with the ground or moving over the ground slower than the wind, and you use the frame of the wind, it is possible to claim ground power, even though it is a bit insane to do so. However, if it is moving faster than the wind over the ground it must have some source of energy other than the ground or the wind as it is doing work on both. It would be losing kinetic energy to the ground and to the wind, not gaining energy from either one.

 

[A.T.]

In the frame of the wind before it encounters the blades of a garden variety wind turbine, what (besides the correct answer "ground") powers the wind turbing.

Sure you can look at it that way if you want to drive yourself batty.

It only drives YOU batty, because it clearly shows that in the reference frame of the airmass, it is the ground that powers the windmill. And that contradicts your key claim, that the ground cannot provide energy in any frame. Without that unsupported assertion you have nothing, and that drives you batty.

 

[profpangloss]

That's odd -- set an anemometer on the belt of a long treadmill and set the treadmill at 10mph. What do you suppose the readout of the anemometer will say?

JB

The anemometer is moving with the tread as a brick, yes? That is not the case with a cart standing still or advancing so your example is not applicable to the case we are discussing here.

 

[profpangloss]

It only drives YOU batty, because it clearly shows that in the reference frame of the airmass, it is the ground that powers the windmill. And that contradicts your key claim, that the ground cannot provide energy in any frame. Without that unsupported assertion you have nothing, and that drives you batty.

No. My claim is the ground cannot provide energy to a cart to make it move against the relative motion of the ground and you have provided no evidence to contradict that, only batty claims about reference frames.

 

[A.T.]

However, if it is moving faster than the wind over the ground it must have some source of energy other than the ground

There are land yachts that move faster than the wind over the ground. What is their power source in the reference frame of the airmass.

 

[ThinAirDesigns]

The anemometer is moving with the tread as a brick, yes? That is not the case with a cart standing still or advancing so your example is not applicable to the case we are discussing here.

You're bobbing and weaving - stick to your assertions until you prove them right or they are proven wrong.

You said that a treadmill can't produce wind of significance. I maintain that a treadmill can create a wind of the same velocity that the tread moves relative to the air. If the treadmill speed is set at 10mph, an anemometer on the belt will read a wind of 10mph.

Do you now agree that a treadmill DOES create wind equal to it's speed setting and that this wind can be measured by an ordinary wind instrument?

JB

 

[profpangloss]

There are land yachts that move faster than the wind over the ground. What is their power source in the reference frame of the airmass.

Do they move directly down wind?

 

[A.T.]

the ground cannot provide energy to a cart to make it move against the relative motion of the ground

The treadmill shows that it can.