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

[spork]

Wow, sometimes it's entertaining - other times it's just depressing.

 

[RossFW]

Just a quicky,

Humber, you DO acknowledge that KE varies with velocity, and as velocity is relative, varies withe the velocity of the observer?

You say that the cart has no KE on the treadmill. You realise that if the cart is rolling down the road, and you are running beside it at the same speed, it has no KE relative to you either, and that this is indistinguishable from the situation were you and the cart are stationary with the cart on the treadmill?

 

[humber]

Actually, what he's referring to is that if the lift were wide enough, you could hang a plumb-bob from each end and measure the difference in the angle at which they hang, or if the lift were high enough you could compare the readings from an accelerometor on the floor and an accelerometor on the ceiling to determine whether or not the lift is accelerating through space or sitting on the ground.

But for a normal sized lift, there would be no measurable difference.

Yes, Brian-M. That's right. Why?.
This point concerns only measurement. Acceleration cannot be shut out, even if you can't measure it.

Same goes for the hobo. It there is a moon, it will feel its gravitational pull, which will appear as strain in the structure or objects within the van.

There is just no point to this argument. Let's say the hobo simply states "I am going 50mph West". How are you going to contradict him, without breaking your isolation? Then he would "know". On the other hand, it makes not difference to him anyway, because as far as he is concerned, there can be no consequences of that velocity at all.
How can that ever be in the real world? It can't be, so you can't use it to make a model. That's the point, not hobos and Einstein.
Despite what you have said, I can see only that windspeed condition is the hypothetical model has been taken literally in application.
How can a mechanical model ever become a literal "box car".

What if I equip the hobo with an aerofoil, such that when he jumps, he gains some forward motion. Now he won't land in the same spot. So what?
Put him in a vacuum? Is the world in a vacuum? Are you now going to add the general restriction that the hobo may not redirect the energy of his muscles, or gravity?

What on Earth has this idea to do with a windcart on a treadmill? You are arguing about ideas of frames of reference, and how they may be described or interpreted, but what has this got to do with the cart?

I don't think you can test the hobo model to make the point, so you need to test the treadmill model. To do that, you must include all of the real-world things that have been simply ignored in the hypothetical model. Then what? If you say, yes, that is what windspeed is, a "box" around the treadmill or cart, how can it react with what is outside the box? I suppose that you must put that in the box to arrive at reality?

It seems to me, that the only connection, is that it allows it to be said that "you can't tell" one wind condition from another. But you can.
If you can simply accept that frames have nothing to do with the treadmill, and just look at it as a machine, (which is what it is) you will realise that the model is nothing like it claims to be, and some claims are even impossible.

 

[Modified]

Just a quicky,

Humber, you DO acknowledge that KE varies with velocity, and as velocity is relative, varies withe the velocity of the observer?

You say that the cart has no KE on the treadmill. You realise that if the cart is rolling down the road, and you are running beside it at the same speed, it has no KE relative to you either, and that this is indistinguishable from the situation were you and the cart are stationary with the cart on the treadmill?

He recognizes it, but claims that it doesn't mean what everyone else thinks it means because it is "only notional", "too simple", or represents "cartoon physics".

 

[humber]

All of your tests had already been denied by reality.

Please show me an oil barrel that travels at waterspeed.

You thought wrong because you don't know what the cart is doing.

If you mean I am not fooled by toys, yes.

You've been asked many times to show where they are different. What wind pushing on the cart is different? What wind relative to a fixed point on the surface is different?

The laminar flow is in the opposite direction of the tailwind.
From the side of the treadmill, the laminar flow moves right to left with the belt. while the air above is stationary. Arithmetically translate that to beltspeed, and the laminar flow will remain in opposition to the tailwind. It is not consistent with real wind. I have more.

 

[humber]

Wow, sometimes it's entertaining - other times it's just depressing.

While you are simply entertainment.

 

[jjcote]

You say that you have mathematical skills, so why do you not use them to deny my argument concerning drag?

Because I can't many any sense out of the things that you say, and you don't listen. On a good day, I can diagram your sentences but although they follow the rules of English grammar, they don't actually have meaning. On a bad day, I can't even parse them. When any of us tries to actually explain something, you respond with nonsense.

I believe I started here by saying that my interest in DDWFTTW is in seeing what kind of explanations help various people understand how it works, similar to my interest in the Monty Hall problem. But you were right, spork, that humber is a special case and no explanation is going to help. On the educational question (though not the physics or engineering questions), I admit defeat.

 

[Modified]

The laminar flow is in the opposite direction of the tailwind.
From the side of the treadmill, the laminar flow moves right to left with the belt. while the air above is stationary. Arithmetically translate that to beltspeed, and the laminar flow will remain in opposition to the tailwind. It is not consistent with real wind. I have more.

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.

 

[Dan O.]

The point is, humber, that the cart cannot tell the difference between being on the treadmill or being on the road. In both cases, the cart experiences the same forces.

The only significant difference will be the scale of the wind shear boundary. In neither case does this boundary layer assist the cart.

 

[spork]

On a good day, I can diagram your sentences but although they follow the rules of English grammar, they don't actually have meaning. On a bad day, I can't even parse them.

It's like you're channeling my thoughts!

But you were right, spork, that humber is a special case and no explanation is going to help. On the educational question (though not the physics or engineering questions), I admit defeat.

This is one of those things I'd love to have been wrong about. I actually enjoy teaching. But I've come to realize I only enjoy it when people are curious and open minded. humber reminds me of a couple of my favorite quotes:

"The greatest impediment to learning anything is knowing everything."

and...

"There are two kinds of people in the world - those who need no explanation, and those for whom no explanation will help"

 

[Dan O.]

Please show me an oil barrel that travels at waterspeed.

That isn't an answer.

If you mean I am not fooled by toys, yes.

You fool yourself.

The laminar flow is in the opposite direction of the tailwind.
From the side of the treadmill, the laminar flow moves right to left with the belt. while the air above is stationary. Arithmetically translate that to beltspeed, and the laminar flow will remain in opposition to the tailwind. It is not consistent with real wind. I have more.

You don't know what you are talking about. http://en.wikipedia.org/wiki/Laminar_flow

 

[spork]

The only significant difference will be the scale of the wind shear boundary.

Yes, but this is not a "treadmill vs. real-world" distinction. It's a small vs. big distinction. If my treadmill was really big it would have just as much gradient as the "real world". Similarly, if I conducted my experiment on a long flat table-top outdoors, I could minimize the gradient.

 

[humber]

Just a quicky,

Humber, you DO acknowledge that KE varies with velocity, and as velocity is relative, varies withe the velocity of the observer?

Not a quick answer, I am afraid. It is more than just that idea.
Yes, RossFW, zero KE, but it is simply a tautology of Newton. It has no consequence at all. In the sense that I am sure you mean, Newton is "relativistic".
None of you have managed to tell me how this is relevant, except that it can perhaps support the "reference frame" idea at windspeed, but this is not supportable in the real world.

Now is it not absolutely so, that if a boat has no velocity relative to the water, then every molecule must be in some kind of time warp? How can that not be the conclusion? They cannot move relative to each other without moving relative to the boat. That is just impossible! Why don't all rivers do this, even if there are no boats in it? Don't evade the question!

You say that the cart has no KE on the treadmill. You realise that if the cart is rolling down the road, and you are running beside it at the same speed, it has no KE relative to you either, and that this is indistinguishable from the situation were you and the cart are stationary with the cart on the treadmill?

In the real world, there is KE for both the cart and the runner w.r.t the ground. Now it is true that when at the same velocity, there is zero KE w.r.t each other, but that KE common to the ground remains for each object. The runner will certainly know about that if he runs into a wall.

On the belt, the "runner" is alongside the cart, but he will have zero KE w.r.t the (real) ground, and the cart. So where is it? W.r.t the belt?
It is not possible, I think, to transfer the KE that way. What is the belt's KE? Can you say that it has the same KE as the cart "would have" on the road. How do you justify that?
What if you make a belt, that has sufficient power and friction, but is essentially massless. What now? The cart would still do its thing at windspeed, regardless.
If you follow this through, you will see that the solution that gives you none of these problems, is to realise that the belt is not the ground, but the equivalent of moving road, set in the ground. Set the treadmill in the ground, and then all zero KE's are the same. So now, the wind is definitely made by objects being carried through the still air by the belt, so that is what is expected.

If you think about the rolling orange, would it matter in which direction it traveled along that belt, in order to gain KE relative to the ground? Only when it is stationary w.r.t the ground, does it have zero KE. What would convince you that that orange was going at the speed of the wind?
It would take a good salesman in my case.
Oranges do that, believe me. What if it were a dip in the belt (it's not) that causes it to spin like that?
OK, the orange makes a dip in the belt to stay fixed relative to the ground with no KE.
So that means it is not at windspeed, whereas in the same situation but without a dip, it is?

It all "works" for two objects "stuck" in the same frame, but a third object moving relative to that, is just as Newtonian as you would expect.

 

[humber]

That isn't an answer.

You are right. It is a request for you to provide information to support a claim not found in nature. Extraordinary claims, require extraordinary proof.

You fool yourself.

If you think about it, that implies mind-body dualism. How quaint.
Another idea dredged from antiquity.

You don't know what you are talking about. http://en.wikipedia.org/wiki/Laminar_flow

I looked but I could not find a comparison between a treadmill belt and a road.
However, my test does. So perhaps you can please address that.

 

[Dan O.]

Yes, but this is not a "treadmill vs. real-world" distinction. It's a small vs. big distinction. If my treadmill was really big it would have just as much gradient as the "real world". Similarly, if I conducted my experiment on a long flat table-top outdoors, I could minimize the gradient.

Yep. That's why I said it's an issue of scale.


Humber somhow thinks that this boundary layer causes the cart to travel up-belt. (Does humber even know which way the belt on a treadmill runs??) The boundary layer is going to be moving with the belt and therefore pushing the cart down-belt opposing the forward movement of the cart just like on the road where the boundary layer is moving with the road.


I wish the forum rules would allow me to answer that question humber asked earlier.

 

[humber]

Yes, but this is not a "treadmill vs. real-world" distinction. It's a small vs. big distinction. If my treadmill was really big it would have just as much gradient as the "real world". Similarly, if I conducted my experiment on a long flat table-top outdoors, I could minimize the gradient.

No, you can only make that claim if the edges of the belt can be shown to change the shear where the cart is. Your toilet paper test shows this to be adequate, though quite clearly flowing with the belt, and so against the said tailwind.

 

[Dan O.]

No, you can only make that claim if the edges of the belt can be shown to change the shear where the cart is. Your toilet paper test shows this to be adequate, though quite clearly flowing with the belt, and so against the said tailwind.

And how is that supposed to help the cart?

 

[humber]

Yep. That's why I said it's an issue of scale.

Humber somhow thinks that this boundary layer causes the cart to travel up-belt. (Does humber even know which way the belt on a treadmill runs??) The boundary layer is going to be moving with the belt and therefore pushing the cart down-belt opposing the forward movement of the cart just like on the road where the boundary layer is moving with the road.

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.

I wish the forum rules would allow me to answer that question humber asked earlier.

Don't let me stop you. Go ahead.

 

[humber]

And how is that supposed to help the cart?

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.

 

[humber]

It's like you're channeling my thoughts!

Like?

This is one of those things I'd love to have been wrong about.

You do love being wrong.

I actually enjoy teaching. But I've come to realize I only enjoy it when people are curious and open minded. humber reminds me of a couple of my favorite quotes:

"The greatest impediment to learning anything is knowing everything."
and...
"There are two kinds of people in the world - those who need no explanation, and those for whom no explanation will help"

And those who have no explanations.