Down wind faster than the wind

[John Freestone]

I get to choose. That's what equivalence "means". If a break none of the rules of physics while doing so, I am at complete liberty to "chose that frame"
Yes indeedy, "all frames are equivalent".

Yep. All reasonably considered frames are reasonably equivalent, excepting real-world problems like limits of scale (the horizontal extent of the 'ground' when that ground is a moving treadmill, for instance).

Being that the Earth is nearby and has massive gravity, and both my real world cart and the treadmill are fully engaged and immersed in the effects of that, I may as well use the ground as any other. It's more convenient.

1. The treadmill and 'real world' cart are indeed immersed in the effects of Earth's gravity. The fact that the tread is an equivalent frame depends on it. If we put a treamill in zero G, the wheels wouldn't maintain sufficient traction on the tread. However, if we put it on an aeroplane (ignoring lower gravity at altitude for now) doing a steady 1000 mph, the cart would behave exactly the same as in a room.

2. It's not more convenient. The equivalent treadmill frame is. That's why they used it.

It seems to me that you are making the same mistake as followers of Post Modernism. They deny an absolute "realty" ( all PM words are in double quotes) and so infer that all views of reality are the same. This is obviously not the case, unless you think that Newton's view is equal to that of those that preceded him. In this thread, "all views are equivalent" seems to mean that any view is equivalent, yet to think that is is stupid of me to use the ground, yet that objection denies your own claim, unless you think you have "a better one".
The problem is not of that, but in assuming that the treadmill is one of those "equivalent" views.

As for KE. It is not relative in the same way as velocities are.

Ah, I think I see what you're getting at. KE is a function of speed, irrespective of direction. That's an interesting point, and I have to say I don't understand how we square that kind of thing when we make frame changes.

My intuition tells me that k.e. should be a function of velocity, not speed, and relative in exactly the same way as velocity, but that may be wrong. I can also understand that there may be some absolute value for velocity in the universe, contrary to what I was saying before (and I'm certainly not meaning it in a postmodern sense). However, to ascertain whether a body is absolutely at rest would seem to involve the measurement of the speed of light in a vacuum, since (I think) every other velocity is relative, and by then we're at the kinds of scales that don't really affect little carts on the surface of a planet, surely?

Even at much greater masses and velocities, the differences are negligible. We might say that a meteorite smashes into a planet, or a feather falls to its surface, but gravity doesn't care whether the planet is smashing into the meteorite, or falling up at the feather. If I hold a prop still and move the air past it, or hold the air still and move the prop past it, we might quibble about kinetic energy, but seriously, does it make a blind bit of difference to the actual physical outcome in either case? Don't the molecules behave identially with respect to each other? Aren't these equivalent frames?

Hold on to your hats, we might be close to having an actual conversation, humber.

To view the world in this way is primitive, and indeed anthropomorphic.

It seems the other way round to me. Being able to see relative viewpoints isn't anthropomorphic. Saying that you can choose any you like, but sticking with Earth seems so.

Perhaps on another planet, where light is poor, its creatures would have perhaps evolved senses to "see" acceleration, or momentum.

We have them in addition to sight. We have accelerometers in our ears, and nerve endings in our skin. They can't tell the difference between equivalent frames either. If a passenger in a car with eyes closed is drowsy and forgets whether he's moving or not, he won't at first be able to tell whether the car has just been driven into something solid, or something solid has crashed into the front of the stationary car. What's more, if the cops couldn't inspect the road carefully, but only inside the car, they'd not be able to say which either.

Viewing the treadmill, they may exclaim "WTF! Where's the momentum gone?"

I think you're getting stuck in the Earth view again. Maybe we're making a subtle mistake in calling it the treadmill's frame of reference. It is the tread's frame of reference; you realise that, don't you - the tread surface is taken as the origin. On the treadmill, stationary w.r.t. the tread they'd see the 'momentum' whizzing past them, and feel the wind in their hair.

Put as gyroscope in the real windcart. Model that on the treadmill. What happens? Does it stop?

I'm not sure what you mean. Lower a gyroscope onto the cart on a treadmill, and it would behave as any gyroscope would behave. Lower one from a helicopter travelling at windspeed over the cart on the ground travelling at windspeed, ditto. What difference would you expect?

Sol, perhaps you can help me again with KE (or anyone, I mean). Doesn't humber have a point? We generally discuss forces, velocities and acceleration as vectors, don't we, and we can describe them as positive or negative. Is KE only positive or zero? What gives?

 

[humber]

Exactly! You finally got the point! You've repudiated all that nonsense you've been saying!



And..... back down into the gooey humberian morass of incomprehension we slip. All within the span of one post...

Oh well.

Nope. Answer the question. Use the subscript if you wish. An an object in motion wrt the ground that has no more KE than the same but motionless object.
Oh yes, you say that you are an expert is one field. Isuggest to you that pilot knowledge may bias the result, leading to a false conclusion. I say that is so, because information and entropy are connected.
A rat that randomly searches its environment will starve, but it uses its intelligence to put the balance in its favour. You don't see the connection or the anthropomorphism of the experiment, because your understanding is limited. Like a young boy who finds a Playboy magazine...

Anyway, I know your technique, so answer the question please.

 

[fredriks]

Really? Then your maths is wrong, because it should. V = 0, so KE = 0?
The first translation is a vector, right? When KE =1/2MV^2, where is your vector?
You didn't put a scalar zero in there did you?

Humber, KE in standard physics is a scalar... I though a physics genius like you would known this.

KE=0 in a reference frame don't implies the same in standard physics as it does in humberian physics.

Last time Fredriks. If you mention the slipping again, you are on "fast scroll". I do not have to supply your understanding.

trust me when I say that I don't think I can learn any physics from you.

 

[humber]

{
I'm not sure what you mean. Lower a gyroscope onto the cart on a treadmill, and it would behave as any gyroscope would behave. Lower one from a helicopter travelling at windspeed over the cart on the ground travelling at windspeed, ditto. What difference would you expect?

Sol, perhaps you can help me again with KE (or anyone, I mean). Doesn't humber have a point? We generally discuss forces, velocities and acceleration as vectors, don't we, and we can describe them as positive or negative. Is KE only positive or zero? What gives?

Simple question. If a moving cart can suddenly lose its KE, when it is said to be actually traveling. What happen to a gyroscope under the same conditions? It can be in a cart or not. If you grab a gyroscope, and force it to move, what happens? Why can a cart get away with that?

You say that the cart and ground are equivalent views. I agree. Buit not that the treadmill is.
OK, we are in the cart with the ground passing backwards beneath.
For our purposes, we need not consider sound, so we leave that out of our model, but we should go back to the ground to check that if we omit it there, we do not cause any problems. It seems not.
The scenery, also, quite OK in both cases. Continue this process until there is only mass, velocity and KE remaining. So, we get rid of the KE from the cart. Back on the ground, CHAOS! Ooops, model too simple.
Reductio absurdum.

 

[humber]

Humber, KE in standard physics is a scalar... I though a physics genius like you would known this.

KE=0 in a reference frame don't implies the same in standard physics as it does in humberian physics.



trust me when I say that I don't think I can learn any physics from you.

You have more than amply demonstrated the latter. And if it is a scalar from a vector, how can you make it relative?

 

[sol invictus]

Sol, perhaps you can help me again with KE (or anyone, I mean).

Sure.

Doesn't humber have a point?

Are you feeling OK?

We generally discuss forces, velocities and acceleration as vectors, don't we, and we can describe them as positive or negative. Is KE only positive or zero? What gives?

KE is the square of a vector - that is, if the velocity of something with mass m is [latex]$\vec v = (v_x, v_y, v_z)$[/latex] in some frame, its kinetic energy in that frame is [latex]$KE ={m \over 2} \vec v^2 = {m \over 2} (v_x^2 + v_y^2 + v_z^2)$[/latex]. As you can see it's positive definite - zero only if all the components of v are zero, otherwise positive.

When you change reference frames to one moving at velocity [latex]$\vec v_0$[/latex] in the original frame, the velocity in the new frame of something with velocity v in the original frame is [latex]$\vec v' = \vec v - \vec v_0$[/latex]. That changes the KE, obviously, and not linearly. For example, if we choose [latex]$\vec v_0 = \vec v$[/latex], the KE in the new frame is zero. In general, the new KE is [latex]$KE' = {m \over 2} \vec v'^2 = {m \over 2}( (v_{x}-v_{0x})^2 + (v_y-v_{0y})^2 + (v_z-v_{0z})^2) $[/latex].

Nevertheless the laws of physics are identical in the new frame - in particular the (total) energy is still independent of time. That's why you can pick any frame you want, do an analysis, and then transform back to the frame you're interested in.

Anyway, I know your technique, so answer the question please.

What question - why there's no subscript? For precisely the reason you said before you contradicted yourself in your own post. You can pick any frame you want, and the value of the KE depends on that choice. In particular you can always make it zero by choosing a frame that moves with the object in question. Sometimes it's convenient to do so, sometimes it isn't.

 

[Dan O.]

I don't think there is any area that hasn't been covered. Some pretty bright folks have been thumping this melon for a while now. JJ is clearly a sharp guy taking a logical path - but that's what will trip him up. humber is completely logic-proof.

I'm just enjoying the insanity. But I'll admit this - there's something I haven't yet figured out about humber. He knows some big words, and sometimes uses them correctly. Does he actually have some form of intelligence in an area far removed from physics, or is he in fact an entire class of psychology students that are performing sublte experiments on the rest of us by posting inconsistent and inane theories about "physics"? We may never know.

I think humber entered this thread after doing some preliminary calculations that proved that a such a cart could not function as claimed. He entered with the smugness that he knew the answer but wasn't going to share how he arrived at that answer. His arrogance now prevents him from admitting even to himself that he was wrong. What started as a simple error in logic or assumptions has now evolved into a serious mental block. Humber's reality depends on the cart not working and as we chip away at the false foundations he has laid, he is being confined to an ever more precarious position. His frantic attempts to climb out of trouble by grasping at concepts from other fields is just taking him further from the safety of the ground state. There are of course solutions to such mental predicaments. One solution is complete mental collapse. It's a fast trip back to reality but isn't very pretty.

 

[jjcote]

So, you didn't answer my question (perhaps you missed it because it was at the end of a page):

First, let's think about the test area. We can used a toothed rail if need be, but I'll suggest we just go with a nice high-traction rubber surface. To start out, our test area will have limited visibility -- it's dark and foggy, and you can see only as far as your flashlight will shine. We're standing on the rubber surface where our cart is going to run, and there is a steady 10 m/s breeze blowing by, in a uniform direction. Will this be acceptable for a test area, or do you feel that you need to see more of our surroundings?

There is a slim chance that I would send an email to Mark Drela. If I were to do so, what sort of simple question could I ask him that you would find persuasive, humber? I'm thinking along the lines of the following:
"Some guys have built a little wind-powered cart that ostensibly travels directly downwind at faster than windspeed. In order to demonstrate it in controlled conditions, they are running it on a treadmill in a room with still air. They hold it in order to let the wheels and propeller spin up to belt speed, then release it, and it accelerates and advances on the belt. From a physics perspective, is this a relevant and valid demonstration of their objective?"

 

[spork]

The difference is that humberian physics only "work" in the humber frame but standard physics works in all frames if you know what you are doing.

Sadly, humberian physics doesn't work in ANY frame. These bizarre notions humber proposes simply have nothing to do with real physics in any frame.

That's a thought - write a short statement about the fact that the treadmill experiment proves the cart goes DDWFTTW. Get humber to agree that if Dela agrees with the statement, humber will admit he was completely wrong all along, will eat humber pie, and will stop polluting this forum with gibberish. Then (and only then) it might be worth sending it to Dela.

Normally, I think that idea would be swell. But we can't get humber to even answer a simple question, or propose a simple experiment and prediction. There's simply no way on earth humber will come up with a statement worthy of troubling Mark Drela over. If such were possible, I'm confident we wouldn't need to bother Drela in the first place.

 

[sol invictus]

Normally, I think that idea would be swell. But we can't get humber to even answer a simple question, or propose a simple experiment and prediction. There's simply no way on earth humber will come up with a statement worthy of troubling Mark Drela over. If such were possible, I'm confident we wouldn't need to bother Drela in the first place.

Oh, I didn't mean humber should write it - that would be a very bad idea, I agree. I meant jjcote (or you) could, and then make sure humber agrees to what I proposed before asking Drela.

Of course I'm sure he won't agree any more than he would bet with you over the physics of the cart. He knows he's wrong, and being proven so in such a definite way would make it much harder to troll.

 

[fredriks]

You have more than amply demonstrated the latter. And if it is a scalar from a vector, how can you make it relative?

Here is one idea. Go to a library, find a book with mechanics in the title, read the book and try to understand what is written in it.

 

[Marcus]

I don't get this slipping/non slipping. It is not only that I still don't know if the wheels go faster or slower compared to the non slipping case.

I also don't see the relevance at all. There are no problem if someone manage to have a slipping cart going faster than the wind. There are no reason to say, ok, the cart works but you are cheating because it is slipping or the weight are to low or something similar.

Humber claimed that wheel slippage was somehow accounting for the performance of the cart on the treadnill, a claim that is testable. Since this claim seems to have been withdrawn, I agree slippage is irrelavant.

I suspect that this will be the fate of any claim that proves to be testable.

 

[Christian Klippel]

Anyone noticed this?

I make no extraordinary claims. Any of the measurement systems known to man can measure velocity.

Let's see. Last time i used my digital oscilloscope, it told me all sorts of things about voltages, frequencies, time, averages and so on. However, it never told me about velocity. For some strange reason, my digital multimeter also doesn't know about velocities, only volts, amperes, ohms, dB, lux and so on. Oh, and my clocks don't know velocity either, they only know seconds, minutes and hours. Anybody here with different experiences?

So, to me it is an extraordinary claim to say that "Any of the measurement systems known to man can measure velocity." But then, humberian physics as a whole is, uhm, let's call it extraordinary. Others might prefer the saying "completely wrong".

Greetings,

Chris

 

[fredriks]

[latex]$\vec v = (v_x, v_y, v_z)$[/latex]

Of topic but why do some subject areas use ugly arrows above letters to show that it is a vector? It usually follows from the context if it is a vector or not.

 

[Michael C]

Just for fun, I made a new video. Some people thought I was cleverly tilting the ruler one way or the other to determine the direction of travel of the cart, so I made a little demonstration to show that that's not the case. It doesn't bring anything new to the DDWFTTW debate, but for your pleasure I'll put it here:

 

[sol invictus]

Of topic but why do some subject areas use ugly arrows above letters to show that it is a vector? It usually follows from the context if it is a vector or not.

They're like Hebrew diacritics - good for children while they learn.

 

[GreyICE]

Of topic but why do some subject areas use ugly arrows above letters to show that it is a vector? It usually follows from the context if it is a vector or not.

Because it's immensely important? And I do mean immensely. Also math really isn't a topic of implied concepts.

 

[fredriks]

Because it's immensely important? And I do mean immensely. Also math really isn't a topic of implied concepts.

I doubt this. I have read a lot of control theory, mechanics, signal processing, mathematical system theory and similar subject and the use of arrows or bold notation differ but it is mostly non existent in control theory.

Control theory is a lot about differential equations, vectors, matrices and mechanical systems and I don't see any problems with the notation used.

 

[humber]

<snip>

Yes. Now please give me an example as requested.

 

[humber]

Double post