Merged DDWFTTW in a “Real” Wind

[humber]

Oh, now I see why you are confused. You think that the "motion of the planet" has some bearing on the situation. It doesn't.

The road, cart, my imagined cars, and the treadmill are all moving along with the planet. This movement doesn't affect how the cart works or why the treadmill is a good analogy. The treadmill represents the movement of the cart over the road (or the road under the cart), not the "motion of the planet."

-- Roger

That's a good one. A road that is not part of the planet.
The TM is therefore a model of a cart, on a belt, on a planet.
But the planet has the gravity.

To correct for that, the TM belt must be massive enough to have gravity.
Walmart are currently out of stock of that item.

 

[69dodge]

What is powering the cart on the treadmill is the belt spinning the wheels.

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.)

 

[profpangloss]

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

If I need to describe every possible situation this will be a very long discussion. Let us stick to what we are talking about and that is a cart on a treadmill that is either standing still or advancing on the tread. I don't care what wind a brick on the treadmill may see as it is not relevant to this discussion.

 

[profpangloss]

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.)

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. 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.

 

[A.T.]

Do they move directly down wind?

Your ad hoc objections, based on unsupported assertions, contained nothing about directions so far. It is just a simple question:

What is the power source of a faster than wind land yacht in the reference frame of the airmass?

Why are is so afraid to answer it?

 

[profpangloss]

That's a good one. A road that is not part of the planet.
The TM is therefore a model of a cart, on a belt, on a planet.
But the planet has the gravity.

To correct for that, the TM belt must be massive enough to have gravity.
Walmart are currently out of stock of that item.

I'm relieved to see there is someone here who understands the significance of the gravitational force of the planet on the cart on the road.

 

[profpangloss]

Your ad hoc objections, based on unsupported assertions, contained nothing about directions so far. It is just a simple question:

What is the power source of a faster than wind land yacht in the reference frame of the airmass?

Why are is so afraid to answer it?

Do they move directly down wind?

Why are you so afraid to answer that?

edit: you do see that DDWFTTW up on the top of the thread don't you?

 

[ThinAirDesigns]

If I need to describe every possible situation this will be a very long discussion.

It can be a very short discussion if you will stay on topic.

We say we have a wind powered cart operating on a treadmill. You say that a treadmill can't make wind.

Does a treadmill set at 10mph create 10mph of wind or not?

How much more to the point can we get?

JB

 

[humber]

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.

But the old pull the tablecloth from under the gravity-held-dinnerware works, no matter what barefoot physics says.

The TM is an elaboration of that amusing gimmick. Some never seem to tire of championing the wonder, and even relentlessly and unmercifully phone academics to tell them of it.

 

[69dodge]

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.

How is it doing work on the air?

It has a propeller that's blowing air backward relative to itself. But the air is moving forward relative to the ground. So, relative to the ground, the propeller is slowing the air. Therefore, in the reference frame you seem to prefer, namely the one in which the ground is stationary, the air is doing work on the cart, not the other way around.

 

[profpangloss]

It can be a very short discussion if you will stay on topic.

We say we have a wind powered cart operating on a treadmill. You say that a treadmill can't make wind.

Does a treadmill set at 10mph create 10mph of wind or not?

How much more to the point can we get?

JB

The answer is NO. It does not make any wind for the cart that is standing still or advancing on the treadmill and that is what we are discussing, right? If you want to talk about a cart moving backwards with the tread, it holds no interest to me at all.

 

[profpangloss]

How is it doing work on the air?

It has a propeller that's blowing air backward relative to itself. But the air is moving forward relative to the ground. So, relative to the ground, the propeller is slowing the air. Therefore, in the reference frame you seem to prefer, namely the one in which the ground is stationary, the air is doing work on the cart, not the other way around.

Would the air be doing work on the cart if the propeller were not turning? It seems the cart must do work on the air in order for the air to have any effect on the cart. And to do that work 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. It is doing a lot of work for something that has no energy source!

 

[A.T.]

Do they move directly down wind?

I don't see anything about directions in your claim:

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

You have also failed to provide any support for that claim.

 

[ThinAirDesigns]

The answer is NO. It does not make any wind for the cart that is standing still or advancing on the treadmill and that is what we are discussing, right?

Wind is the relative motion between air and a surface. If the wind is blowing across a lake or a plain, it's blowing for ALL. No different, a treadmill either makes wind or it does not make wind. It can't make wind for one device on it's belt and not make wind for another.

Do you agree that a treadmill set at 10mph makes 10mph of wind and this wind can be measured by a garden variety wind instrument?

JB

 

[profpangloss]

But the old pull the tablecloth from under the gravity-held-dinnerware works, no matter what barefoot physics says.

The TM is an elaboration of that amusing gimmick. Some never seem to tire of championing the wonder, and even relentlessly and unmercifully phone academics to tell them of it.

Yes that is a good comparison and one of the few examples of friction doing positive work. The treadmill is another example of that. Nothing to do with wind power.

 

[Modified]

The answer is NO. It does not make any wind for the cart that is standing still or advancing on the treadmill and that is what we are discussing, right?

Wrong. By wind we mean air movement relative to the surface. If the cart is at the speed of the air, then it is at wind speed.

 

[humber]

"In this case the cart gets its energy from the treadmill."

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.

Thoughts turn to a bull in a china shop hoping that earplugs will reduce the damage.

.

 

[profpangloss]

Wind is the relative motion between air and a surface. If the wind is blowing across a lake or a plain, it's blowing for ALL. No different, a treadmill either makes wind or it does not make wind. It can't make wind for one device on it's belt and not make wind for another.

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.

Do you agree that a treadmill set at 10mph makes 10mph of wind and this wind can be measured by a garden variety wind instrument?

JB

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

 

[profpangloss]

Thoughts turn to a bull in a china shop hoping that earplugs will reduce the damage.

.

Yes I thought so too. Very odd.

 

[profpangloss]

Wrong. By wind we mean air movement relative to the surface. If the cart is at the speed of the air, then it is at wind speed.

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