If you get anything that approximates something intelligible from humber buy a lottery ticket immediately.
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Split Thread The validity of classical physics (split from: DWFTTW)
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If you get anything that approximates something intelligible from humber buy a lottery ticket immediately.
Brian-M
Daydreamer
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Edited by Gaspode:
Edited for rule 12
Do not use personal attacks to argue your point.
Replying to this modbox in thread will be off topic Posted By: Gaspode
You say that all the time, even implicitly stating it in this very post where you claim you never said that.
Let me remind you...
See? By claiming that is is not the same, you are implicitly stating that it is different. The reason for this alleged difference remains unknown to the rest of us because you have yet to provide us with any coherent explaination for why it's different that stands up to even rudimentary scruitiny.
If you have a Direct Downwind Faster Than The Wind cart that is travelling faster than the wind, then yes. You can slow it down so it is travelling backward relative to the air (by using with a fork, spork or whatever eating impliment is close to hand) and it will regain it's lost velociy.
That's exactly what Spork is doing in the videos, reversing it's direction relative to the air. From the viewpoint of someone travelling at windspeed (ie, standing on the ground beside the belt) it just looks like the cart is going backwards. From the perspective of the belt (which is all that really matters) the cart is still going forwards, just slower.
But of course, you don't believe that there could possibly be a real DDWFTTW cart, so this answer is purely hypothetical, from your perspective.
Video #7? This Video #7? The video where Spork deliberately tilts the treadmill to keep the cart stationary?
The same video where Spork posts in response to a text comment:
The applied force here is something called GRAVITY. By tilting the treadmill upwards, GRAVITY is pushing the cart backwards.
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Yeah - I know others have asked. Mender also I think, in some form anyway. But in his recent response to me humber certainly made it sound like he thought he had a clear idea of how the F1/BMW tunnel worked (even if I grasped only fragments of it), and he also said he thought it was a correct or valid model (some words to that effect). Given that, I can only assume that if he is not a troll then he will be able to describe a way to do the test? If...!It's a good question, but not a new angle. But then again, he never directly answered this question when I asked it. Maybe you have more luck.
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Christian Klippel
Master Poster
Hello Clive,
you're really an optimist, i would say.
But then, the hope dies last
Greetings,
Chris
No, the difference in velocity between the boundary layer and the wind is fixed. It does not change with the velocity of the observer. The motion of the observer is common to both flows. A flow parallel to that, but 'followed' by an observe not in that wind itself, would register the same result. Maybe you think I can't do arithmetic Brian_M, but I do understand the principle of superposition.
The colored smoke test says that no matter how you would express it on the treadmill, that condition cannot happen in real wind. Relative velocities are irrelevant if one stream does not exist.
I submit the balloon or kite for your consideration. The retarding friction of the road is a result of the applied force. If the applied force is great enough to overcome the static force; a reaction of the motionless wheels, the object will move forward. At this point, the friction falls sharply, becoming that of the rolling friction. This distinction is what allows locomotives to pull much more than their weight. Early locomotive engineers did not know this, relying only on their intuitions about friction, leading them to use unnecessary geared tracks, and even mechanical feet.
The object "feels" easier to push once moving, but not because less force is required per se, but that the conditions changed during that process.
No, I mean that friction to the road is not necessary for the wind to move an object, whereas on the treadmill, it is. That is clearly a difference.
But you agree that the only apparent difference, is that on one case the wheels spin, and in another they do not?
The maths is too elementary to be considered useful, and the logic behind its application is flawed.
The road cannot drive the propeller in the way you describe, Brian_M. That is, the cart cannot benefit by using the difference between the prop and the ground or whatever. The prop, cart and wheels are one object, coupled to the road.
Unless the wheels spin excessively and lose traction, the cart can be considered part of the road's surface. The wind blows over this surface, and that is the only differential velocity available.
Consider Micheal_C's first video. When the 'top' ruler is moved, the paper beneath the wheels is also moved. Note that what you are seeing is the differential motion of the left and right hands, but they are common to the ground through Mr_C's body.
There is no equivalent on the cart, but there is on Ynot's turntable, because of the tether. These mistakes are fundamental, yet repeated.
Michael C
Graduate Poster
It's a good question, but not a new angle. But then again, he never directly answered this question when I asked it. Maybe you have more luck.
I did H'ethetheth, but you kept insisting that the treadmill and BMW/F1 are similar.
No. If there is wind, that is entirely different. Remove the wind, and it's not just a case of less windspeed, but no model at all.
The answer, as I wrote in the BMW/F1 case, is that the belt and wind are equal but opposite. So 100kph wind, means belt goes backwards at that same speed.
Do you think this is true?
A car in the driveway has a belt running under it, so that is passes under the chassis and so between the wheels. The car is not at beltspeed.
If you lift the car on to that belt, so that it spins the wheels, it is the same as if it were traveling at beltspeed.
You know, your own treadmill proves my point. If you stand on the running belt, you will see the cart moving away from you.
As I said, if the moment you step on the belt, you mentally expand the belt to an infinite plane, there is no motion between you and the belt, so there can be no motion between the cart and belt.
The reason is that the belt mimics only the surface of the road, so when the belt is expanded to be what it is said to approximate, a boundary free plane, you see only what is attached to that plane.
There is only you, the cart, and the boundary air layer, and nothing else. There is no moving belt, so there can be no motion between you and the cart or even the boundary layer. You can move around, and there will be no up belt or down belt and the cart will remain motionless to that plane.
This is part of your own idea about isolated frames of reference!
When you step on the belt as you currently do, then you are effectively seeing other frames. You are looking "out of the window" to see a relative motion that is not strictly available from the belt.
Expansion of the belt, cuts off those views, and you see only what is in that frame. In "beltworld" all the KE's and velocites and so forth are once again normal and Newtonian. When correctly applied, you will see that from ALL frames, the cart is motionless.
TAD et al, do not know what the F'k they are taking about.
Micheal_C, this is not Zen. I can simply ask you to nominate one case, of your choice, leaving the other to become the complement. That would still leave you to explain the difference. When you reject the absolute, the difference becomes that absolute by default.
Nested irony alert!
More chance than you have of understanding it.
Michael C
Graduate Poster
No, this is not Zen: I asked you a simple question: in which case do the wheels spin? Please give a simple answer: is it the car parked on the belt, or the car parked on the road?
OK Clive, but I thought your comment on the Russian puzzle to be bizzare, so I assumed that ended it. It is legitimate. I have the book. A chance discovery.
"Physical Paradoxes and Sophisms" V.N. Lange. MIR Press.
Russian ed. 1978, Translation 1987. That makes it 31, not 27 years ago, as I previously stated.
I have referred to the treadmill as a Sophism, and that word caught my eye when scanning a table of 2nd hand books. The rest you know.
Why do you do that Micheal_C? All the information that you need it there.
You decide. On the floor on jacks, what ever.
Does putting the car on the belt make it move at windspeed, and what is the difference between any other form of car and wheel spinning combination?
No nonsense, please.
This is what I'm interested in humber. This is why I've asked you to describe the configuration required (in your opinion) in the F1/BMW tunnel to test a cart travelling at 10 mph over the ground in the same direction as a 10 mph wind. That's a wind isn't it? We want wind. Be the wind. Make the wind. I don't care... just tell me how you would set it up in the tunnel, and then we can talk about if we agree or disagree or whatever.
Maybe you don't think the F1/BMW tunnel can be used to test things going downwind? Or maybe you think it can't be used to test things going downwind at precisely the speed of the wind? I'm only asking you to tell me what you think about this, and if you can see how to do it, then give me the details.
Should we start with something else. I don't mind. Maybe this is easier: how about the cart going downwind at 5 mph with a 10 mph tailwind. Will you explain how to do that one for me if the other is too difficult for some reason? It doesn't have to be a perfect model - just tell us what you think is wrong with it if you do see some flaws.
That's great. Perhaps my earlier comment was too hasty. I'd certainly like to be able to read what the book says about the similar-to-DDWFTTW problem you mentioned. As I also mentioned earlier, your original post about it contained a broken link to an image of some kind. Was that a page scanned from the book or something else? Perhaps you can post it again?
H'ethetheth
fishy rocket scientist
Yes.
That doesn't actually mean anything.
It appears you do, at least partly.
Wrong. For a sufficiently large treadmill, the flow is identical for equivalent observers.
Yes.
No. On the treadmill as on the road, friction between road and wheels is necessary to propel the cart to speeds larger than windspeed.
No.
No.
No.
No.
In some ways yes, in other ways no.
No. All of the cart is moving relative to the surface, except a very small part of the wheel.
Yes, just like on the treadmill.
Depends on the observer.
No
What?
There is.
No.
Repeated, yes. Mistakes, not so much.
The direction of the wind is not so important as its presence in each case.
The headwind is the major application of the BMW/F1 system, so I used that. So, the answer is, a 10mph wind is met by a 10mph belt in the opposite direction to that wind in each case.
So a tail wind is met by the same. In fact like the condition assumed to exist on the treadmill. That is not the reason that I say it is "backwards". That condition occurs because there is no real tailwind. If there were, then the treadmill would be OK.
This is different from the case where the object on the belt generates its own wind by motion with the belt, as is the current situation, which demands that the cart move with the belt.
If the cart is on a motionless belt, it can make a self-generated headwind by motion in either direction. Once the belt is in motion, the direction of the "wind" becomes indeterminate. It can be tail or headwind, dependent upon the ratio of cart-to-belt-speed and belt-to-air-speeds. Some combinations are valid in what is physically realistic, and some not.
This is to crack a walnut with a sledge-hammer. Real world motion cannot be simulated by a belt. It is not done on any treadmill, of any sort.
I have been through all of them, including the human runner.
This is true of the BMW/F1 setup. The belt simulates the passing of the road surface "under" the car, but not the motion of the car.
One difference is immediately apparent. The belt 'surface' is cyclic, a pattern would repeat. If that were done, do you think that will cause F1 race tracks to be that way? No, of course not. So why do you think it 'forces' a car to move in the 'real' world?
Re: The book. Sorry, I misunderstood your remark. I thought you were suggesting that it was a sham, because of the faux Russian author you ascribed to it.
But that is the correct link. It is scanned from the book, which is pocket sized, so it spreads over a few pages. If you can't read it, I can scan it again or perhaps try an OCR.
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It does. The flow is a fixed velocity less than the wind. And object moving in that wind at 5kmph, adds/subtracts to the main wind as much as it does to the boundary wind at any point in the profile, including ground. (leaving only the motion of that object w.r.t ground.) The difference between the main wind and the boundary layer, is a fixed offset for all velocities.
The smoke test proves that there are two flows. Punt.
You are mixing models and equivalency. Models do not exploit this. The treadmill does, but incorrectly. You can see this. If you to stick to your interpretation (which is correct) then the belt is the road, but not the ground or Earth. That last step requires the belt to be an "equivalent" plane.
The model that you have in mind, is like the BMW/F1. A belt set in the ground. That means that the treadmill-side observer is the ground, as all of the sane engineers present, will aver. Once again, the cart is not moving in any frame. The belt is not a road, but as you say, a surface simulation.
On the road, it is necessary to provide a reaction to the force from the propellor, but only to that directed to the ground. The cart can move using the propellor as a sail, regardless. On belt, it is necessary to pick up energy from the wheels, to gain any at all. Big difference.
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If you do not want to know, it does not bother me, H'ethetheth.
I do not do this Brian_M. I do not need to twist your words. If you make a hypothetical case to support yours, and I refute it, then you can not simply go back and say I misinterpreted it. I am saying you are wrong, that is what I am saying.
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