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

[RossFW]

So where is it? W.r.t the belt?

It is any where and has any value, depending on the difference in velocity between the cart and the observer.That's what relative means. Run on the belt at belt speed (Zero KE, right?) Now attach a brick wall to the belt. It will hurt just as much as if you ran into a stationary wall attached to the ground. STOP running on the belt, match velocities with the wall, you now have zero KE RELATIVE to the wall, and it doesn't hurt a bit!!

What is the belt's KE?

RELATIVE TO WHAT? It has a different KE depending on the difference in velocity between it and whetever datum you choose to pick. Like every other mass in the universe!!

If you think about the rolling orange,

Where was it that frictionless Oranges were grown again?

 

[Dan O.]

Does he?
No, the laminar flow is slower at the ground, so the average velocity of the flow is less than the wind, but it travels in the direction of the wind, but slower. The difference is that treadmill wind is opposite to the cart at full winspeed and not the difference between windspeed and the average velocity of the laminar flow layer as a whole. That is not same.
Humber thinks that this is an indicator that the model is not good.

Try putting yourself on the cart (running down wind but not up to wind speed yet. You are facing forward, the main wind is at your back pushing you and the cart forward. Reach your had down to feel the wind just a centimeter or two off the road. Which way is that wind going? Now try the same thing on the belt.

 

[humber]

If by "laminar flow" you mean slower wind in planes near the surface, those effects are exactly the same on the treadmill or ground. Wind speed at ground level will be, relative to the surface, in the same direction as the wind at higher elevations but at a lower speed.

Not quite Modifed. If you imagine a band of air, say, 1 cm above the belt,
it definitely moves slower than the wind, but in the direction of the wind. Let's say it's 90%. At standstill in wind, the flow moves downwind at 90% of windspeed realtive to the observer. At windspeed, it is slower than the cart, but still at 90% windspeed w.r.t the road. It is an easy trap to thing of "lagging behind" as going backwards.

A person going back with the belt, sees the flow initially as zero w.r.t the belt. However, when moving up the belt, the flow is not lagging, but opposite the direction of travel. It looks right at windspeed, but that is just because the numbers cancel out.

 

[humber]

Try putting yourself on the cart (running down wind but not up to wind speed yet. You are facing forward, the main wind is at your back pushing you and the cart forward. Reach your had down to feel the wind just a centimeter or two off the road. Which way is that wind going? Now try the same thing on the belt.

Yes, it is some velocity less than the cart, but not going backwards.
Pick a speed of a vehicle moving up the belt at less than windspeed, then the laminar flow is definitely a headwind, moving opposite to the vehicle's motion.

 

[humber]

It is any where and has any value, depending on the difference in velocity between the cart and the observer.That's what relative means. Run on the belt at belt speed (Zero KE, right?) Now attach a brick wall to the belt. It will hurt just as much as if you ran into a stationary wall attached to the ground. STOP running on the belt, match velocities with the wall, you now have zero KE RELATIVE to the wall, and it doesn't hurt a bit!!

No, you can change that according to how well the object is connected to the belt.

RELATIVE TO WHAT? It has a different KE depending on the difference in velocity between it and whetever datum you choose to pick. Like every other mass in the universe!!

First measure the KE of the belt. Put the cart on the belt. The cart has zero KE, so preumably the belt's KE must change, to make up the KE for real windspeed. If the belt's speed is fixed, as is its mass, how can it change according to the mass of the cart?

Where was it that frictionless Oranges were grown again?

Leeton, Victoria, Australia. Take a look.

 

[spork]

Not quite Modifed. If you imagine a band of air, say, 1 cm above the belt,
it definitely moves slower than the wind, but in the direction of the wind. Let's say it's 90%. At standstill in wind, the flow moves downwind at 90% of windspeed realtive to the observer. At windspeed, it is slower than the cart, but still at 90% windspeed w.r.t the road. It is an easy trap to thing of "lagging behind" as going backwards.

A person going back with the belt, sees the flow initially as zero w.r.t the belt. However, when moving up the belt, the flow is not lagging, but opposite the direction of travel. It looks right at windspeed, but that is just because the numbers cancel out.

It's times like these that I begin to question whether humber is just messing with us. I'm willing to give him credit for being pretty friggin' clueless, but my hermit crabs could get this one right.

 

[humber]

It's times like these that I begin to question whether humber is just messing with us. I'm willing to give him credit for being pretty friggin' clueless, but my hermit crabs could get this one right.

No, think of it this way. In real wind at windspeed, the laminar flow is slower than the downwind; it lags the downwind. If you "pause" the cart, that flow will catch up to you. Do the same on the belt, and the laminar flow moves further away, except for at exactly windspeed, (where you can't "pause" the cart)

 

[RossFW]

No, you can change that according to how well the object is connected to the belt.

OK, now you are just being deliberately dim. Obviously exactly the same thing could be said about how well the wall is attached to the ground.

Right or wrong do you actually want a rational discussion, or to deliberately be a pain in the butt?

 

[Dan O.]

Yes, it is some velocity less than the cart, but not going backwards.

Are you not familiar with the Wind profile power law^WP? The wind at the ground has zero velocity relative to the ground. So if the cart is moving at any forward speed, there is a layer of air near the ground that is moving backwards with respect to the cart. This hold for both the cart on the road and the cart on the treadmill. The difference is that this gradient is compressed on the treadmill because there is less surface area interacting with the wind.

 

[spork]

spork: It's times like these that I begin to question whether humber is just messing with us....

Humber: No, think of it this way....

Yup - he's just trying to mess with us now. I checked with the Bob's. One of them got it right away. The other initially got it wrong, but then felt really dumb when he realized his mistake.

 

[John Freestone]

No, think of it this way. In real wind at windspeed, the laminar flow is slower than the downwind; it lags the downwind. If you "pause" the cart, that flow will catch up to you. Do the same on the belt, and the laminar flow moves further away, except for at exactly windspeed, (where you can't "pause" the cart)

That's been dealt with before. Can you please try to think about the following statements: If you 'pause' the cart in 'real wind', what that means is that you stop it, i.e. make its velocity wrt to the ground zero. Now, if you do the thought experiment on the treadmill, trying to maintain the right equivalences, when you pause the cart, you can't just imagine it stop w.r.t. the room. That is measuring velocities from different frames of reference in the same scenario. Do you see? To check the equivalence, you can 'pause' the cart on the treadmill only by thinking of its velocity as zero wrt the belt. You see the equivalence: ground=belt, not ground=room carpet? It is tricky to imagine, because you must suddenly see your cart on the treadmill zooming off backwards wrt the room, but if you contemplate this you will see that it is correct, and the wind that hits you as you zoom off the back of the treadmill is a tailwind, and its gradient to where it meets the belt has the same sense as on the road.

Next, you have been reminded of your own drawing that showed the gradient in the same sense. How do you explain that? Are you right now, or were you right then?

Finally, once again, do you really think that little old you, on the one hand, is right, when your view is at odds with everyone else (apparently) on this forum, and contrary to all the current uses of treadmills for testing things from formula one race cars to god knows what, and contrary to the explicit laws of physics since Galileo?

 

[humb]

I checked with the Bob's. One of them got it right away. The other initially got it wrong, but then felt really dumb when he realized his mistake.

Bob1 and Bob2? Are they not men? No wonder you think that asking them would be a good analogy; like humber and myself, they've got you jerking back and forth!

 

[CORed]

Now that you ask, it may well cause a problem for the cart as far as friction to the belt goes, but I was thinking that it does not help the treadmill's claim of equivalence. Yes, that is what I was thinking.

No. At most, it shows that the treadmill does not perfectly model some minor effects that have no significant effects on the performance of the cart.

 

[humber]

OK, now you are just being deliberately dim. Obviously exactly the same thing could be said about how well the wall is attached to the ground.
Right or wrong do you actually want a rational discussion, or to deliberately be a pain in the butt?

I am right, and I and trying to have a rational discussion, RossFW!

When the cart is taken from windspeed, it is mentally "box-cared" to show the relationship that you say exists.
It is agreed that the boxcar is a reduced environment to show the "important" effects? Yes, but when on the belt, you need to restore the connections that sustain those effects.
We can say the velocity requirement is met by the belt's motion, so that leaves the KE. You agree the cart's KE w.r.t the ground is zero. To be a valid model, it must be there, "relative" to something. The only candidate is the belt.
How is it possible that the belt can do this? Simply the speed is not enough, because the mass must be included to make the relative relation correct.

I can see know means of calculation, other than to simply say it "must" be so, yet it cannot be measured to sustain that claim.
If you take a KE measurement from the belt, it will not be correct. How can you do that, without causing the cart to loose it position of zero KE w.r.t the ground? Like the runner!
I have tried to do this test RossFW in anticipation of your objections, yet it always fails. Even moving the cart a little from an imaginary vehicle will fail, because the cart will gain that KE relative to the ground and the belt.
(That is why the fork moves the cart)

This is a least a part of what I have been trying to tell you. Zero KE objects cannot interact with the environment, yet remain at zero KE relative to that environment. True, but of no use.

 

[humber]

Are you not familiar with the Wind profile power law^WP? The wind at the ground has zero velocity relative to the ground. So if the cart is moving at any forward speed, there is a layer of air near the ground that is moving backwards with respect to the cart. This hold for both the cart on the road and the cart on the treadmill. The difference is that this gradient is compressed on the treadmill because there is less surface area interacting with the wind.

You are suggesting that you cannot walk because the bottom layers of your shoes do not move relative to the ground?

No, that is not correct. If the cart is in real wind, it is immersed in the wind, not at the leading edge of it. There will be wind ahead and behind the cart.
This cart is like an object immersed in a river, but close to the bed. The water flows slower at the shear layer, but not backwards. That can happen, but it is usually a contraflow created by an obstacle, and the flows may even be equal and opposite.

This situation can occur for the belt. The laminar flow can be sen to be equal and opposite to the velocity of travel, which is the case at "windspeed", though the relationship changes at different velocities w.r.t the belt.
This is not the case in real wind. The flow is never reversed.

The belt laminar flow is a contraflow, it "slips under" the air of the room, which is said to be a tailwind. Therefore, it is wrong.

 

[humber]

Yup - he's just trying to mess with us now. I checked with the Bob's. One of them got it right away. The other initially got it wrong, but then felt really dumb when he realized his mistake.

Good. That will be Bob's Institute of Higher Learning? Perhaps there is an Arby's at MIT?
Not Bob, but you, You tell my why one of your pupils is wrong, and the other right.

 

[humber]

Finally, once again, do you really think that little old you, on the one hand, is right, when your view is at odds with everyone else (apparently) on this forum, and contrary to all the current uses of treadmills for testing things from formula one race cars to god knows what, and contrary to the explicit laws of physics since Galileo?

Has it not occurred to you, John, that if a number of people learn the same error, it is not unlike one person making the same error?

F1 cars do not use treadmills in this manner. Interestingly, the world still works the same, before and after Galileo. Also, if you had said "information theorem" to him, he may have said "Whata isa that?

ETA:
The drawing is a profile, not a flow. I made that clear

 

[humber]

Bob1 and Bob2? Are they not men?

Your not fussy are you?

No wonder you think that asking them would be a good analogy; like humber and myself, they've got you jerking back and forth!

[/QUOTE]

More lube.

 

[RossFW]

F1 cars do not use treadmills in this manner.

No, but their designers DO use windtunnels, with the car stationary and a "Wind" produced, to simulate the car movingh through still air.

THEY understand it is a model of the real situation, YOU don't.

Zero KE objects

ZERO KE RELATIVE TO WHAT?? You STILL don't get that KE is RELATIVE!! There is no such thing as a "Zero KE" object EXCEPT to an observer matching velocities with it. Conversely, ANY object is zero KE to ANY observer at the same velocity as the object, REGARDLESS of what else the object may have relative velocity too. The surface of the Earth is in NO WAY a special frame of reference. If two media are moving relative to each other, it is ONLY the velocity difference that matters, NOT which media appears to be moving to a third party observer.

 

[humber]

No. At most, it shows that the treadmill does not perfectly model some minor effects that have no significant effects on the performance of the cart.

Not the point CORed. You know that I claim that the cart largely stays at windspeed because of friction. That friction is a result of gravity and the coefficient of friction to the belt. The cart is light around 150g/5oz, so the force is not large. The laminar flow will tend to lift the cart and wheels, reducing it even further. The main point though, is that is shows some other problems with the system. It is an indicator that something is not right.

Do you agree that it is flowing the wrong way?