Do you think that there are no spacial frames of reference? If you go to the top of The Empire State, and put yourself on a treadmill, do you think that will somehow effect the taxis at street level? Really?
Down wind faster than the wind
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Do you think that there are no spacial frames of reference? If you go to the top of The Empire State, and put yourself on a treadmill, do you think that will somehow effect the taxis at street level? Really?
but humber, nothing whats over in this thread suggest that you understand anything about physics.
I have an idea if you actually understand what a reference frame is, use a couple of sentences to explain it to us so. It is possibly that at least some one take you a little serious if you at least once show that you understand something.
I have an idea if you actually understand what a reference frame is, use a couple of sentences to explain it to us so. It is possibly that at least some one take you a little serious if you at least once show that you understand something.
Doesn't it at all bother you that the treadmill is entirely inconsistent? Now, I can adopt your views that the treadmill IS a frame of reference, yet it fails.
Sometimes, objects get stuck on flat conveyor belts. I have seen oranges do this. They spin, on the belt, in roughly the same place. I think they have eccentric axis of rotation and c.o.g. Is that orange also going at windspeed?
Humber,
Imagine that (with some supernatural being's help) we've arranged for the following idealised testing environment:
Earth has been essentially replaced with a giant billiard ball, thus having a perfectly flat surface (insofar as we use the term "flat" on earth), but it still has essentially the same size, mass, and gravity, as the earth, plus an atmosphere that is similar in terms of composition and so on. Let's say the rest of universe is completely empty. No sun, no stars. (But we'll allow ourselves torches or similar so we can see what we're doing!)
We've also arranged so the southern hemisphere can rotate independently of the northern hemisphere - as if the earth had been cleanly sliced in two through the equator and then the two halves put back together again with a frictionless interface between them. You can imagine a long shaft running through the north and south poles and thus joining the two halves if that helps but shouldn't really be necessary! We also have things set up so the southern hemisphere is rotating (from west to east) slightly faster than the northern half so that a person standing just south of the equator and looking north will see the northern hemisphere apparently moving right to left (east to west) at 10 mph, even though the northern hemisphere is still rotating at the usual earth rate - something close to 1000 mph at the equator if my quick calculation is correct.
In addition we have a perfectly smooth and constant speed air flow moving around the globe from "west to east", at exactly the same speed as the southern hemisphere at the equator but also sufficiently far to the north and south of this also for the purposes of any cart testing we may want to do in that area. So this air flow is like a belt around the earth's equator and it's speed matches the speed of the ground in the southern hemisphere in the equatorial regions.
I'm presuming that you're happy to accept that the slight curvature of the earth's surface, and similar very small effects that come from that (plus missing stars and sun, etc) are not significant enough to make a difference in terms of testing a cart like spork's on this version of earth. But please tell me if this presumption is incorrect, and if so what the problem is. I agree there could be extremely minor effects, or difficulties with getting the "perfect test environment" from some of this, but I haven't seen you raise this earlier so it seems likely that you agree we can ignore these issues unless unless perhaps we ended up looking at a cart where the difference between possible success and failure of some test was extremely small. Spork claims his cart can comfortably beat the wind, so that doesn't appear to be a likely scenario. We're not using General Relativity either are we?
Finally, let's say you are standing right in the northern hemisphere, close to the equator, and I am standing near to you (for now) but on the southern side of the equator. We will be moving relative to each other though because the two hemispheres are moving relative to each other. We both also have a spork type cart, exactly the same in every important respect.
Before we move onto testing the carts, can you please confirm that this description is clear. Please tell me if you would feel any "real wind" where you are standing in this idealised world (just north of the equator), and in which direction and speed it might be blowing. And what would I be feeling at my position just across the boundary in the southern hemisphere? Is that "real" also or not? Does any of this set-up suffer from the problems that you see with the treadmill tests?
Humber, you never did reply to my post #2240 (quoted in full above), even though I reminded you of it again later. I'm hoping you will respond this time.
I'm not really interested in quibbles over whether my use of wording like "a perfectly flat surface" implies the wheels of the cart won't grip and so on. Try to see past any errors or bad wording of that kind and understand the big picture that I am trying to paint. The point of this that I want you to see is that "you" (in the northern hemisphere in this scenario) are standing in a "real wind" on an earth-like planet in terms of its mass and rate of rotation and so on. In this same scenario I (standing in the southern hemisphere) am standing in exactly the same air mass yet I feel no wind because the air mass is not moving relative to me.
Imagine now that I lean across the divide between the two hemispheres and place my cart facing towards the right on the ground (which is moving right to left at 10 mph relative to me), hold it in place until the wheels and prop are "up to speed", and then release it. I claim this is exactly the same as placing my cart on a giant treadmill (made out of half the earth). As I see it, the surface is moving right to left but the air above that surface is not moving relative to me.
Also imagine that at the same time as I am doing this, you put your cart on the ground facing in the same direction as mine (in other words east, or downwind as you feel it) and then (by hand if necessary) accelerate the cart up to wind speed. Say we also coordinate our efforts so that your cart reaches wind speed at the same moment mine is ready to be released and the two carts are side by side at that moment. We both release our carts. Will they behave differently? Why?
I claim I am effectively using a big treadmill to test my cart but that you (from your perspective standing in the northern hemisphere) have no reason to claim you are not in a "real wind" on the earth like system. Yet the two carts are side by side, and I say they must perform identically after being released. If spork and JB's videos are anything to go by and the carts we are using have the correct specifications, then they will accelerate at that point.
What aspect of this hypothetical test is significantly different from using a more conventional treadmill, and why?
sol invictus
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Failed again... you could be moving away from the carts, in which case accelerating one towards you will decrease its KE.
Don't worry, the fifth time's the charm.
Crash it into what, humber? The amount of energy released is determined by the characteristics (both mass and velocity) of the object and the thing it crashes into.
How, after so long, do you still manage to fail so completely to grasp these trivial concepts?
Modified
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I'm not sure what you are talking about. In both cases, air above the surface is at a certain speed (with respect to the surface), but near the surface it is slower due to drag. The short length of the treadmill may reduce that effect, but the difference is minor.
But again, you keep using the ground reference frame as equivalent in both cases, which it is not, since it does not bear the same relationship to the surface, air, or cart. You can do all computations for the cart on the road from the reference frame of the wind, in which, to use your terminology, there is "no wind", and do the same computations for the cart on the treadmill from the reference frame of the wind (which is the same as that of the room in that case). The computations and results will be identical. What you can't do is use the surface reference in one case and the wind reference in the other, and claim that since KE, etc. is different so the two situations are not identical.
The flaw is quite simple, as I have said. The ground has a different relationship to the surface and air in the two cases. You use it as if it had the same relationship to the surface and air in the two cases.
No, you don't. Newton's laws say nothing about the local surface of the earth being a special frame of reference.
Again, you are mixing reference frames. A fork held at wind speed will produce the same collision energy in both cases (very gentle in the case of the cart traveling slightly above wind speed). A fork held at surface speed will produce the same collision energy in both cases (fairly energetic in the case of the cart traveling slightly above wind speed). You can't compare a collision with an object at wind speed in one case to an object at surface speed in another and require them to be the same.
How can you not? Computations such as KE and momentum are relative. You are using two frames of reference that do not bear the same relationship to the air, surface, or cart, and pretending they are the same.
No. My Doppler gun is fixed to the tower. If a place my barrier half way between the cart launch site and the tower, I get a lower registered KE than I place the barrier at the tower. The doppler radar can be used to calculate the acceleration and velocities of both carts.
I told you it's a buffer. It absorbs energy. Railway engineers appear to have no trouble with the concept. They have been in use for more than 100 years.
If that's a bother, I will think of something else.
But of course, no matter what the result, the treadmill cannot reproduce it.
sol invictus
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As far as I can tell, your claim now is that if you accelerate something from zero to non-zero velocity, it gains KE.
Wow! Stop the presses - what an amazing revelation!
Sorry, humber, I'm tired. I could repeat myself for the umpteenth time and try to explain to you that the energy released in an inelastic collision depends on the mass of your buffer and its velocity as well as the mass of the object and its velocity, but it's pointless.
I'm done.
CORed
Penultimate Amazing
Question 1: I don't have any idea what you mean by "spacial frames of reference". and I'm pretty sure you don't either.
Question 2: Welll um ...... No. Though I can only guess what part of your anatomy you pulled this entirely irrelevant question from.
No, the paper quite clearly shows the belt wind blowing the wrong way.
Maybe, but I can also get the correct calculations my assuming my ground reference, and that the treadmill IS only a treadmill. That cannot be contradicted. I assert it is therefore a treadmill, and the 'windspeed' frame is entirely notional.
If I put a treadmill on the floor and walk to it and then step on it, so as to face down the belt, I will feel a wind against my face. However, I feel the same wind when walking to the treadmill, but I just don't notice it. Effectively, I am just walking faster when on the belt.
An accelerometer will tell me that it is the belt that is moving and not the ground. I find that all windspeed changes correlate with a change in acceleration. This will confirm my that I am on a belt. Knowing that, all the anomalies are explained, and inform me of the true nature of my 'frame'.
The belt is in agreement not with a model of a stationary road with wind over it, the belt passing under the wind, but with a real moving road, in still air.
He does have something to say about objects traveling at 0 KE. The only way that the belt can mimic the KE of a real cart, would be to crash it into a barrier when the cart was going full speed back with the belt. However, my groundside view is entirely consistent. It shows no anomalies, because it is true frame of reference. The belt can also be a frame of reference, but then it is not consistent with the claimed model.
No, I am saying the frame is non-existent.
They are the same. I could be on the belt traveling with it, and play out a line to the cart. I would find that the force required to move it would be the same as the fork. A device attached to the cart as a test fixture, could work locally to the belt and measure that force. It would be the same in all three cases.
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I doubt that. If I convert my KE gained from acceleration in any frame to say chemical energy, the transaction would be the same, no matter where or when I did that. It is independent of frame, but not relative. It stays with the body where it is stored.
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That contradicts the treadmill. Which is why you so strenuously avoided saying it.
Yes, transfer will not be 100% perhaps, but quite clearly, more. The masses are known, so we can build the buffer so the error is negligible. Same problem for the belt, though. So?
It's amazing. You are still asking questions about the concept of frames of reference. I say that it is not possible to reconstruct a frame of reference.
But I can let that go, and still show the idea to be wrong.
You can model the conditions of the frame you are trying to reconstruct. The treadmill is a complete failure in this respect. You don't seem to appreciate how illogical your ideas are, so you concentrate on details, as IF the treadmill were a frame of reference. Its a model, and a bad one.
Please do as I suggested. Walk from the floor onto the treadmill from the usually raised end. Your velocity wrt to the ground increases. However, as you look back, you see that the cart is still where it was, and you are in no doubt that is it stationary wrt the ground. See? It's not moving. It would be almost indistinguishable from one on the floor, right next to it.
Why does it do that? Because it essentially ignores the belt. The belt slips under it, because the friction to it is so low. Connect it to the belt as you are when moving, and it will go backwards. But that is not important, it just shows up another anomaly. It is not a frame of reference, so that really doesn't matter. So what does it say? It says that this cart, responds to being driven into a headwind (like you) by driving itself into a minimum energy state. An orange stays on the belt for another reason. My cart too. (There are many ways of doing that. Can't you think of any? No?)
In wind, if you wear a pair of skates, and launch a parachute so that it carries you down wind. Eventually, you will reach terminal velocity. Strain gauges to the parachute and in the skates, will show forces to be opposite, but at a maximum. That is the real world case for down wind travel.
On the treadmill, the opposite will happen. When you reach 'terminal velocity', you will be stationary as the cart is now. The gauges will show a minimum force. Opposite to the real world, except for the case where you are NOT traveling. That is the correct view of the cart or 'frame', if you must.
Imagine a small battery powered wind cart, where a motor drives a propellor. What do you think that will do on the treadmill?
John Freestone
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Thanks, that was all clear. I actually put 'correct' because when I wrote the sentence at first I also squeezed in a comparison between the frame of reference we keep calling the "treadmill", which we we should perhaps call that of the "tread", but it was confusing so I deleted the other bits and forgot that 'correct' was still there. Actually, I've confused myself now. Maybe that's wrong and what I'm doing is translating back again mentally. If I consider the tread as my frame, I guess that means it is at rest (nominally, of course), and that is not the natural description of the treadmill test, perhaps. Neither, of course, is more 'correct' than the other, but the treadmill test is used precisely so that a 'stationary' cart can be observed, then how it 'accelerates slowly forward'.
When constructing calculations and taking measurements on the treadmill, the cart is released at what the experimenter presumably records as 0 velocity, and so on, and it is only when we translate back that we again imagine the tread as synonymous with the ground outside. That - the tread - then becomes the frame considered at rest, and the cart can be considered travelling downwind at velocity. I jumped back into that frame too soon, perhaps just because I'm thinking of how it does translate back - Ethel the tortoise with the wind in her hair.
Now I think about it, when a cart is moving across a salt flat propelled by the wind, we could describe that from different frames, i.e. choosing different parts of the system to consider at rest and measure velocities relative to. So there is something specifically different between just making different mathematical boosts for the same scenario, and constructing a different one (in gross physical terms - like the treadmill). That too can be described in different mathematical frames.
Because these frames and scenarios are equivalent in all significant aspects, it really does not affect the outcome at all. I may be over-analysing.
But it may also lead to some confusion if people think "land-cart ~ treadmill-cart: that's what different frames of reference are", and don't realise that any motion can be described from any reference point, and that's what frames are. It is that fact which allows experimenters the handy trick of using one scenario to stand for the other precisely.Or they could until today...
John Freestone
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me said:
Sorry, I shouldn't try to guess what you think.
No. But that's Borg's formula, anyway.
Resistance is futile.
You ask questions and make statements with too few specifics for me to parse them. Are you trying to ask me whether resistance is or should be relative to some kind of origin? If so, why? It seems nothing to do with the mechanical question at hand. As in both situations, there are things in the calculations that are left unsaid, like resistance in a circuit is a function of temperature, etc. This is like a workshop in cold reading.
Same problem. Do I think there would be more to what than what? And is there any freaking point to your asking other than to play for more time and piss me off?
One of them is writing things that can be understood.
Tangential to the circumference of the circle it was following while I held the string, I think. Dare I ask if there was any reason you asked that question?
Surely that wasn't the reason. Your point being?....
Incidentally, it seems a rather large proportion of people get the DDFTTW cart question wrong at first. Some never change from that position, come hell or high water.
(@sol, I think)
No you won't. You've never done a single thing you've said. No math, no proofs, no definitions, no predictions, no test specs, NOTHING.
Definitely no need to repeat this. We all know you can't or won't make anything, prove anything, describe anything, define anything, or even make a consistent argument of any sort.
Boy it must suck to have peope throw words back in your face that you've been throwing at us for 50 pages or so.
No comment. I just really wanted to see this in print again.
Seriously Ross, you can't be saying there's anything seemingly intelligent about this troll - can you!? The guy knows a few words, but has yet to put any of them together into a remotely meaningful sentence, and he has the logic and attention span of a rutabaga.
John Freestone
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More great vanishing tricks from the humber:
Humber - why? What in god's name is the possible connection? Extreme example? You said that the cart on the treadmill does what it does (i.e. goes forward) because it gets rid of as much KE as it takes from the tread, and that that is all the prop was doing, just balancing that energy input by getting rid of it. You then said that a flywheel would do the same thing, and later repeated that it was no more than a flywheel on wheels. If it were fastened solid to a bar, it can't move forwards or backwards, can it, and no comparison can be made between the action of the prop and that of a flywheel.
If we, utterly bemused that you could imagine such a thing, ask for confirmation, and you suggest fastening the cart to the frame of the treadmill, how is anyone meant to take than other than more playing for time, trolling, avoiding the day when someone tests another of your predictions and proves you wrong?
Ta-daaaa! No flywheels, no rags, no sticks in place of props. Seriously, spork or JB - have you not yet replaced the prop with a flywheel and put it on the treamill so that humber can dismiss the result as irrelevant? If you have, I've missed the link. We keep asking him if this is still his position, and he still fails to deny it, so we can only assume that it is what he believes. In fact, his first word was 'yes', before he changed the scenario altogether.
Humber - why? What in god's name is the possible connection? Extreme example? You said that the cart on the treadmill does what it does (i.e. goes forward) because it gets rid of as much KE as it takes from the tread, and that that is all the prop was doing, just balancing that energy input by getting rid of it. You then said that a flywheel would do the same thing, and later repeated that it was no more than a flywheel on wheels. If it were fastened solid to a bar, it can't move forwards or backwards, can it, and no comparison can be made between the action of the prop and that of a flywheel.
If we, utterly bemused that you could imagine such a thing, ask for confirmation, and you suggest fastening the cart to the frame of the treadmill, how is anyone meant to take than other than more playing for time, trolling, avoiding the day when someone tests another of your predictions and proves you wrong?
John Freestone
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Sorry, I just have to stop you there.
John Freestone
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Almost at windspeed, usually. Of course, with a complicated object like an orange and a sudden jerk from a checkout conveyor, all sorts of things can happen. In the general scenario, the conveyor belt moves off, but the innertia of the orange has to be overcome if it is to move with the belt, and if the jerk is sudden, instead, the orange is caused to rotate. It's the same as the tablecloth from under the setting trick.
If the shopping moves with the belt, it has the earth-stationary air moving past it. If it fails to move with the belt, it is stationary with the air, or, as we keep repeating, moving at windspeed. In general, it does not stay stationary rotating, but is dragged with the belt a little. The cart without a prop does pretty much the same thing. It moves backwards, but not at belt speed. You predicted as much yourself in a moment of lucidity. What the orange doesn't do is travel "up-tread", against the belt direction, except due to momentary complications that might ensue. It does not make headway in steady state. That is what we observe the cart doing. That is also why a flywheel would not do the same as the prop, unless it were first given excess angular momentum. From a standing start, it would act the other way: its innertia would act as a sort of flexible imperfect brake. And at steady state, it would do absolutely nothing, AFAIK.
Your cloth round the workings would act as a brake linearly and permanently, helping the cart to be skimmed off the treadmill faster than a Jimmy Dean sausage.
Nope, but if humber defines the test and tells us what result he predicts I will do it.
Is there any reason I need to? No.
Am I going to convince every last person in the world? No.
Will I do such a test anyway just because I'm a good sport? Yes - if humber can remain lucid enough to describe the test he wants to see and the result he expects.
That being the case I don't expect to be doing that test anytime soon.
Also, let's keep in mind, I don't hold any great secret. I've done everything I possibly can to make sure others can build and test a cart just like ours. Whether or not I do the specific test that compels any given skeptic should never stop them from doing their own. I assume most folks are aware of the posted parts list, build notes, and even build video series.
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