Split Thread The validity of classical physics (split from: DWFTTW)

[Dan O.]

This is not an important point, and I am willing to concede defeat, but I cannot see how I am wrong.

[qimg]http://www.internationalskeptics.com/forums/attachment.php?attachmentid=12662&stc=1&d=1231651083[/qimg]

This is real wind. The laminar flow is a stack of layers, that slide over on another, yet they always move forward in the direction of the wind.

If the hand is placed so the wind is on the back of the hand, for speeds less than windspeed, I cannot see how the force can ever be felt upon the palm of the hand, if for no other reason than the hand would shield it.

As soon as the same observer moves up the belt, he will immediately feel the laminar flow upon his palm.

The velocity profile of the wind near the surface comes from the fact that at the surface, air molecules are bumping into the irregularities in the surface and therefore do not have an average velocity with respect to that surface and that each microscopic layer of air above the surface layer is continuously exchanging momentum with both the layer below and the layer above it.

This exact same effect occurs regardless of whether the air is being driven by an upper level wind or the ground is being moved as on a treadmill. There will be differences primarily related to nearby objects that are moving at a different speed.

So, if the cart operator is stationary with regard to the surface he will feel a wind on his back with the wind speed decreasing to zero at the surface. When he starts moving, what was a zero speed wind near the surface is now moving relative to the cart (opposite the direction of the main wind). This is true for both the case of the cart on the road and the cart on a moving belt.

 

[Dan O.]

I don't see how you can ask that, Dan_O. What you are saying is what is already understood about relative winds. But in effect, you are asking me to compare two different models.
There are a number of real-wind (windtunnel) treadmill examples, that would apply to your claimed case, but 'the' treadmill is not one of them .

All of the effects I claim are due to failures of that equivalency. They may appear to be detectable as simple differences of veloicty of the wind, or something else.
You insist on following this point, while ignoring the problem that the force of the treadmill wind, regardless of immediate detection, is related to gravity. That is so. The real wind is not like that, and that begets all the other effects.
I still think the laminar flow fits your demands, though. You don't agree, but I can't see why.

I ask that question because this is where your flawed view breaks down.

For the simple case of the cart traveling at the speed of the wind, if the cart is on the road you have air that is slowed by the road moving under the cart. Which way do you see that air moving? If the cart is on a treadmill there is air that is accelerated by the treadmill moving under the cart. Which way do you see that air moving?

 

[spork]

You have no wind to falsify.

Even on fast scroll I find that much of what humber posts consist of gems like this!

I can hardly believe he has us still going with such gibberish after so many pages.

 

[humber]

The velocity profile of the wind near the surface comes from the fact that at the surface, air molecules are bumping into the irregularities in the surface and therefore do not have an average velocity with respect to that surface and that each microscopic layer of air above the surface layer is continuously exchanging momentum with both the layer below and the layer above it.

Yes, but the idea is stylised. There will be turbulence, particularity at the road surface, but that will not extend to the 'top' of the flow. If not, then the flow can hardly be laminar. Of course there is the problem that the forces determining this behavior are not in the boxcar model, but that aside, the air molecules will endure a series of random collisions, but there will still be a drift in the direction of the wind.

This exact same effect occurs regardless of whether the air is being driven by an upper level wind or the ground is being moved as on a treadmill. There will be differences primarily related to nearby objects that are moving at a different speed.

There will be differences related to motion on the belt, yes.

So, if the cart operator is stationary with regard to the surface he will feel a wind on his back with the wind speed decreasing to zero at the surface.

Surely this breaks the "no force at windpeed" hypothesis. We would need to see if that holds for all velocities of the laminar layer. That raises some questions.

When he starts moving, what was a zero speed wind near the surface is now moving relative to the cart (opposite the direction of the main wind). This is true for both the case of the cart on the road and the cart on a moving belt.

No, the real wind follows the cart. This means that the laminar flow it "sees", is the slower wind that is the product of the wind ahead of it. The laminar flow is not 'connected' to the cart, it is a flow, that is below the cart but, slower than at the cart.

No matter what, it comes from behind the cart. That is the direction of the source. The pressure differential of that flow, will indicate the direction of flow to be from the rear of the cart. It is detectable by hand.

The tread mill will say the opposite. That the source is from the front, when going up the belt. No surprise, that is where it comes from.

 

[Dan O.]

Actually, right now I have wind gusts in the range of 80 kph. I'm wondering if I should take the antenna down before it folds over again.

 

[humber]

Even on fast scroll I find that much of what humber posts consist of gems like this!

I can hardly believe he has us still going with such gibberish after so many pages.

Spork fishing.

 

[humber]

Actually, right now I have wind gusts in the range of 80 kph. I'm wondering if I should take the antenna down before it folds over again.

Is that before or after you make your rebuttal to my last post?

 

[Dan O.]

WINDSPEED is not a defined word. If you insist on using words that have no standard definition, you must supply a definition.

 

[humber]

WINDSPEED is not a defined word. If you insist on using words that have no standard definition, you must supply a definition.

it makes no difference, the laminar flow is still wrong when the cart is at windspeed. If you wanted to shield the wheels from the flow, where would you put the shields? On the front. And in the wind? On the rear.
I also find it hard to believe that the laminar flow is going backwards at full beltspeed. This suggests that the laminar flow has no forward (tailwind driven) velocity at all.

 

[Dan O.]

The air closest to the surface is moving at exactly the same speed as the surface in all cases. Do you agree that this is true on the road? Do you agree that this is the case on the treadmill? When the treadmill is stopped? When the treadmill is running at full speed?

 

[humber]

The air closest to the surface is moving at exactly the same speed as the surface in all cases. Do you agree that this is true on the road? Do you agree that this is the case on the treadmill? When the treadmill is stopped? When the treadmill is running at full speed?

I agree that I can tell the difference. Do you?

 

[Dan O.]

What are you thinking of using to shield the cart moving at the speed of the wind from the wind? What does this look like for a cart on the road? What does this look like for a cart on the treadmill? What is the relative velocity between the shield and the cart?

[/invisible]This same question was ignored by humber in the original thread. Will he ignore it again?[/invisible]

 

[Dan O.]

I agree that I can tell the difference. Do you?

You haven't defined what difference you are talking about.

 

[humber]

You haven't defined what difference you are talking about.

I think that I can tell the difference between real and treadmill wind.
Do you agree?

I can gratuitously extend that to including windspeed.

 

[spork]

"You haven't defined what difference you are talking about."

"I think that I can tell the difference between real and treadmill wind.

Yet another completely non-responsive response from the guy that made it famous!

 

[Dan O.]

As I've said, there are going to be differences because the treadmill belt is a finite size. This will cause the gradient of the wind near the treadmill surface to be compressed. This would be easy to detect but it is not material to the operation of the cart. If it is a concern, a larger treadmill could be used to minimize the difference.

As you said, the real wind is driven by pressure differences. There will be an infinitesimal difference in the air pressure over a distance equal to the length of the cart. I don't think you can afford an instrument sensitive enough to measure such a difference.

Other than those, no, I don't believe you can tell the difference. And more to the point, the cart can't tell the difference and will operate exactly the same regardless of whether it's the wind or the belt doing the pushing.

 

[humber]

As I've said, there are going to be differences because the treadmill belt is a finite size. This will cause the gradient of the wind near the treadmill surface to be compressed. This would be easy to detect but it is not material to the operation of the cart. If it is a concern, a larger treadmill could be used to minimize the difference.

It is not material to the operation of the cart. Correct.

As you said, the real wind is driven by pressure differences. There will be an infinitesimal difference in the air pressure over a distance equal to the length of the cart. I don't think you can afford an instrument sensitive enough to measure such a difference.

Yes I did say that.

Other than those, no, I don't believe you can tell the difference. And more to the point, the cart can't tell the difference and will operate exactly the same regardless of whether it's the wind or the belt doing the pushing.

My hand says otherwise.

You put up this challenge,Dan_O. I say I have met that challenge. I say that I can tell the difference between real and treadmill wind by the means I have described.
Do you agree?

 

[humber]

Yet another completely non-responsive response from the guy that made it famous!

Go team!

 

[spacediver]

Did you get that?

the laws of Newton are of the same form in a moving system as in a stationary system, and therefore it is impossible to tell, by making mechanical experiments, whether the system is moving or not.

So, on one hand we have one of the most highly respected physicists of the 20th century, and on the other hand we have you, an anonymous internet user.

Humber I'd like to see a response to this.

Here's the original feynman quote:

If we substitute this transformation of coordinates into Newton's Laws we find that these laws transform to the same laws in the primed system; that is, the laws of Newton are of the same form in a moving system as in a stationary system, and therefore it is impossible to tell, by making mechanical experiments, whether the system is moving or not.
The principle of relativity has been used in mechanics for a long time. It was employed by various people, in particular Huygens, to obtain the rules for the collision of billiard balls, in much the same way as we used it in Chapter 10 to discuss the conservation of momentum.

 

[RossFW]

Yes,yes, yes, but you forget the essence of Humberism....

Newton, Dreler,Feynman, even Einstien didn't say what they said. They say what Humber SAYS they said!!