Down wind faster than the wind

[humber]

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.

Mmm.. Unlike your sleight of hand to introduce a tether. You didn't answer how that would be possible to tether a craft moving at windspeed.

You will need to take a refresher course with Oprah, before making such claims, which are indeed quite wrong.
I see not chipping. You have not refuted one single claim. What happens is that, like the rest, you simply don't answer.

 

[John Freestone]

Sure.

Thanks.

Are you feeling OK?

KE is the square of a vector - that is, if the velocity of something with mass m is

in some frame, its kinetic energy in that frame is

. As you can see it's positive definite - zero only if all the components of v are zero, otherwise positive.

Ah, right. Of course, I was forgetting the squaring stops any negative energy (except in alternative therapy ).

When you change reference frames to one moving at velocity

in the original frame, the velocity in the new frame of something with velocity v in the original frame is

. That changes the KE, obviously, and not linearly. For example, if we choose

, the KE in the new frame is zero. In general, the new KE is

.

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.

Ok. So particular objects will have different energies in different frames, just as they have different velocities. The air in the room, and the cart on the treadmill, from the frame of the Earth (and indeed treadmill body) has no KE (ideally), right?

Presumably, you'd also say that it does have (mv²)/2 from the frame of reference of the tread? If so, it seems that humber's KE discussion is no more and no less than a mathematical repeat of his English failure to see things from that correct perspective of the tread? - since he keeps arguing that the air and the cart have no KE on the treadmill - he's just seeing it from Earth-frame.

I'm still a bit confused about this conversation you had with humber, though:

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.

What I mean is that I would expect that there should be a subscript saying what a velocity, acceleration or KE is relative to, but obviously this might be no more than a convention. You can choose any frame you want, as you say, but that will alter the KE. That would seem to be the only reason a value would need a subscript, to say what frame we've used, although it could be put once and then taken as read. I wonder if you and he are genuinely at cross purposes there, and he's arguing that the lack of one shows that there's only one absolute frame for KE measurements (the centre of the humberverse), hence no qualifying subscript is needed. KE just is what it is. D'you see? Obviously that means that somehow he accepts boosts as they relate to velocities, but not KE, which kind of screws up (mv²)/2.

Oh who cares. Thanks again, I appreciate the lesson. I'm just going to ignore the word 'entropy' for the time being. I can't chase every white rabbit that runs past.

 

[humber]

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

No figurative tests. Just real, practical tests. As I have said, NOT CART, TREADMILL. Really...

There is a slim chance that I would send an email to Mark Drela.

Yes, it seems that contact is waning.

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?"

Yes, that's the sort of thing. Ask him if the cart is traveling at windspeed, or simply balancing on a treadmill as seen.

 

[John Freestone]

....Sorry it took a while to reply, BTW, I was shooting at people on a train for scientific purposes.

 

[humber]

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.

What makes you think I don't already have it...from elsewhere.

 

[humber]

Anyone noticed this?



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

So, while you were reading and typing, it did not occur to you, that given the question was about velocity, I meant any means of velocity measurement known to man?
BTW. From that list of equipment you can. I hope I never have to rely on your resourcefulness.

 

[humber]

... Obviously that means that somehow he accepts boosts as they relate to velocities, but not KE, which kind of screws up (mv²)/2.

No it does not.

Anyway, perhaps you know ohm's law V=I*R. See any reference to What R is?
Do you think that there may be more to it that that?
Of course. There are things that make the difference between someone who can read, and those that can understand.

Perhaps you can think of twirling a mass on a string over your head. Cut the string. Which way does it go? A study taken about 10 years ago, showed that 51% of US physics graduates got that wrong. 51% did no better than those who had no scientific training.

I am still waiting for an example.

 

[sol invictus]

Yes. Now please give me an example as requested.

I already did. But OK, here's another: a 2 kg weight slides on the ice rink at Rockefeller Center in New York, moving NW at 1 m/s. In the frame in which Rockefeller Center is at rest - which is a non-inertial, spinning frame hurtling in circles around the sun and the Milky Way, subject to Coriolis and centrifugal forces - the weight has approximately 1 J of KE. In the (much simpler) inertial frame in which Rockefeller Center is moving in a straight line which coincides with SE at that place and time at 1 m/s, the weight has 0 J of KE.

 

[humber]

I already did. But OK, here's another: a 2 kg weight slides on the ice rink at Rockefeller Center in New York, moving NW at 1 m/s. In the frame in which Rockefeller Center is at rest - which is a non-inertial, rotating frame hurtling around the sun and the Milky Way, subject to Coriolis and centrifugal forces - the weight has approximately 1 J of KE. In the (much simpler) inertial frame in which Rockefeller Center is moving in a straight line which coincides with SE at that place and time at 1 m/s, the weight has 0 J of KE.

I thought you would do that, which is why I wrote "An an object in motion wrt the ground that has no more KE than the same but motionless object."
Pretty clear, no Hebrew.

 

[sol invictus]

Ok. So particular objects will have different energies in different frames, just as they have different velocities. The air in the room, and the cart on the treadmill, from the frame of the Earth (and indeed treadmill body) has no KE (ideally), right?

Right.

Presumably, you'd also say that it does have (mv²)/2 from the frame of reference of the tread? If so, it seems that humber's KE discussion is no more and no less than a mathematical repeat of his English failure to see things from that correct perspective of the tread? - since he keeps arguing that the air and the cart have no KE on the treadmill - he's just seeing it from Earth-frame.

Right - although I wouldn't say the tread frame is correct. It's just that there is an extremely simple map from physics in one inertial frame to physics in another, and it is often convenient for analysis/experiment to pick a different one than the one you really want to study, knowing the results in one frame can be trivially translated to the other.

As in the case at hand.

What I mean is that I would expect that there should be a subscript saying what a velocity, acceleration or KE is relative to, but obviously this might be no more than a convention. You can choose any frame you want, as you say, but that will alter the KE.

The reason there's no subscript is that the formula is valid in all frames. It gives different answers in different frames, but each one is correct. If you say "the KE of Y is X", full stop, you haven't said anything at all - you must specify the frame.

Saying "the KE is X", full stop, is closely analogous to saying "the location of Y is X miles north". North of what? Of course, often you can get away with it because the reader understands what you mean, but obviously Y is also X miles south of somewhere else (unless it's the north pole, I suppose).

 

[sol invictus]

I thought you would do that, which is why I wrote "An an object in motion wrt the ground that has no more KE than the same but motionless object."
Pretty clear, no Hebrew.

That object has zero KE (momentarily), which is the minimum possible. And nothing is "motionless" on earth - there is no inertial frame in which earthly objects are motionless. But if something was motionless in some frame, it would have exactly the same KE (zero) as the object I just described does.

 

[humber]

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.

Your suspicions are correct. Any test that falsifies the treadmill, will not be conducted. The treadmill is not a frame of reference, so it does not matter.

These recent post have raised a question. I think that anything I say, will not chgange your beliefs, and that is what they are.
So what would convince you that the treadmill is BS?
The experimental science is so poor, that I cannot trust that. So knowing that, what would you need to know? Any "thought experiments" perhaps?
Forget Wikki. Just your ideas, against mine.

 

[Christian Klippel]

So, while you were reading and typing, it did not occur to you, that given the question was about velocity, I meant any means of velocity measurement known to man?
BTW. From that list of equipment you can. I hope I never have to rely on your resourcefulness.

If you meant that, then you should write it that way. You wrote "any measurement system". Not "any velocity measurement system". The former means just anything, the latter refers to velocity.

And no, a scope can not measure velocity. It measures voltages, set's them in relation to an internal timebase to get a waveform display. It can do some math on these values, but that's all it can do. A DMM can not measure velocity at all. You might use a scope or a DMM to display the readout of an sensor that measures velocity, but in this case the scope or DMM is merely a display, nothing else. They can not measure velocity on their own. When using a sensor, that very sensor is the measurement system, not the display. A clock can not measure velocity. You need at least some way to measure a distance, and a reference to measure that distance against. Oh, of course an sensor also needs a reference to give its readout any meaning.

If you still insist that a scope, a DMM or a clock can be used to directly measure velocity, go ahead and explain. But then, that is where you fail always: giving explanations.

And the only thing that one can hope for is that they will never ever be in a situation where they have to rely on your broken understanding of physics.

 

[jjcote]

No figurative tests. Just real, practical tests. As I have said, NOT CART, TREADMILL. Really...

Well, you've lost me here. "NOT CART"? It's hard to discuss a cart that goes DDWFTTW without including the cart.
I do want to discuss the cart. I'm asking if a level rubber surface with a 10 m/s uniform wind blowing across it, in the foggy dark, will suffice for a test bed, or if you need to see more of the surroundings to know if it's ok.

Yes, that's the sort of thing. Ask him if the cart is traveling at windspeed, or simply balancing on a treadmill as seen.

Is my question acceptable as phrased or not? If a simple answer to that question will not be convincing to you, propose some wording that will.

I believe you have said that the spork/JB cart will work with something else (flywheel? stick? rag?) in place of the propeller. Is that your position? If so, let's see you do it. spork and JB have built and shown a cart that maintains its position (or if given a more favorable belt speed, advances readily). Let's see you build anything that can be placed on a running treadmill that will not immediately shoot off the back. If you succeed, it's going to look (and work) a lot like the cart in the video.

 

[humber]

That object has zero KE (momentarily), which is the minimum possible. And nothing is "motionless" on earth - there is no inertial frame in which earthly objects are motionless. But if something was motionless in some frame, it would have exactly the same KE (zero) as the object I just described does.

No good. Two objects side by side. I measure all possible sources of velocity and KE from here to the centre of the Universe. This is then my datum.

Now leave one where it is. Using a differential Doppler radar to measure the relative velocities, accelerate one to 1m/s, without increasing its KE above the stationary object. Stationary being defined by my previous datum. Velocity being defined by the radar. KE being defined as the amount of energy stored in the object, which then may be converted to heat and measured with a calorimeter.

 

[CORed]

Your suspicions are correct. Any test that falsifies the treadmill, will not be conducted. The treadmill is not a frame of reference, so it does not matter.

These recent post have raised a question. I think that anything I say, will not chgange your beliefs, and that is what they are.
So what would convince you that the treadmill is BS?
The experimental science is so poor, that I cannot trust that. So knowing that, what would you need to know? Any "thought experiments" perhaps?
Forget Wikki. Just your ideas, against mine.

I think Humber has realized that he was wrong about the wheels slipping (when he said they were slipping) and when he claimed that the slipping of the wheels was somehow improving the performance of the cart, not when he said they weren't slipping or that it doesn't matter). However, it seems that he is pathologically incapable of saying "I was wrong", so saying it's irrelevant is probably as close as he will ever come.

Regarding the treadmill: I can't think of any "thought experiment" that would show me that the treadmill is not a vaild model for the cart at or near windspeed. Doing so would invalidate everything we know about physics back to Gallileo. I realize that Humber for some reason can't grasp that, but, that's his problem, not mine not anyone else's still posting in this thread.

As far as I'm concerned, at this point the only value in arguing with Humber is the entertainment value of the outrageous nonsense he keeps posting.

 

[humber]

Well, you've lost me here. "NOT CART"? It's hard to discuss a cart that goes DDWFTTW without including the cart.
I do want to discuss the cart. I'm asking if a level rubber surface with a 10 m/s uniform wind blowing across it, in the foggy dark, will suffice for a test bed, or if you need to see more of the surroundings to know if it's ok.

Yes, OK. If you insist.

Is my question acceptable as phrased or not? If a simple answer to that question will not be convincing to you, propose some wording that will.

Yes, but I think that he should see the video. Asking one-off questions is difficult. The question should contain the claim that the cart is at windspeed.
I say it is on a belt as you see it, and that is the full extent of its capacity.
It is small vehicle, traveling up a moving belt. That's it. It represents nothing more than that.

I believe you have said that the spork/JB cart will work with something else (flywheel? stick? rag?) in place of the propeller. Is that your position?

Yes, but really if you want to proceed, you are going to have to think what that means. Extreme example. Place a steel bar over the belt, and fix the cart to it, that the wheels spin as before. In other words as it is, but restrained by the bar. Now is that at windspeed. do you think, being restrained like that? I presume you say no.
(1) Do you care about, say, the exact size of the bar?
(2) Why is this not "really" windspeed.

If so, let's see you do it. spork and JB have built and shown a cart that maintains its position (or if given a more favorable belt speed, advances readily). Let's see you build anything that can be placed on a running treadmill that will not immediately shoot off the back.
If you succeed, it's going to look (and work) a lot like the cart in the video.

OK slight change of plan. I will do that. I will show you how to do that very thing. You can make it yourself, if you like, but that should not be necessary, unless you have the mindset of Creationist.
Let this be clear. I cannot make anything, and I do not have to. I am not going to. Do I have to repeat that?

 

[humber]

I think Humber has realized that he was wrong about the wheels slipping (when he said they were slipping) and when he claimed that the slipping of the wheels was somehow improving the performance of the cart, not when he said they weren't slipping or that it doesn't matter). However, it seems that he is pathologically incapable of saying "I was wrong", so saying it's irrelevant is probably as close as he will ever come.

Next slipping wheels reference puts you on fast scroll. I will take it that you are incapable of saying anything else.

Regarding the treadmill: I can't think of any "thought experiment" that would show me that the treadmill is not a vaild model for the cart at or near windspeed. Doing so would invalidate everything we know about physics back to Gallileo. I realize that Humber for some reason can't grasp that, but, that's his problem, not mine not anyone else's still posting in this thread.

So, you have no ideas why you think so, except that someone has told you?
So you say.

As far as I'm concerned, at this point the only value in arguing with Humber is the entertainment value of the outrageous nonsense he keeps posting.

Want entertainment? Go play in the park.

 

[Modified]

Yes, but really if you want to proceed, you are going to have to think what that means. Extreme example. Place a steel bar over the belt, and fix the cart to it, that the wheels spin as before. In other words as it is, but restrained by the bar. Now is that at windspeed. do you think, being restrained like that? I presume you say no.

Yes, it is still at wind speed. The bar did not change the speed of the air in the room. The bar is also moving at wind speed. This is equivalent to the cart on the ground at wind speed being restrained by a bar that is being constrained to move at wind speed through some mechanism, such as being fixed to a belt that is moving at wind speed. The cart will behave the same in both situations.

 

[sol invictus]

No good. Two objects side by side. I measure all possible sources of velocity and KE from here to the centre of the Universe. This is then my datum.

Now leave one where it is. Using a differential Doppler radar to measure the relative velocities, accelerate one to 1m/s, without increasing its KE above the stationary object. Stationary being defined by my previous datum. Velocity being defined by the radar.

I can do better - with that setup I can decrease the KE of one, leaving the other alone. Choose a frame in which the two objects are moving at 1 m/s in the opposite direction you're going to accelerate towards. Then, as you accelerate it, the one you act on will have its KE decrease to zero.

KE being defined as the amount of energy stored in the object, which then may be converted to heat and measured with a calorimeter.

That definition makes no sense whatsoever. You cannot covert KE to heat without acting on the object with something. But depending on the characteristics of that something, you can generate arbitrary amounts of heat. For example, if the object rubs against the surface of a very massive object (like the earth), friction will eventually bring it to rest wrt that surface. But depending on the relative velocity of the surface to the object at the beginning, any amount of energy can be converted to heat.