There is only one quack here.
Split Thread The validity of classical physics (split from: DWFTTW)
- Thread starter Dan O.
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There is only one quack here.
I think you're bluffing. Do try the treadmill test. See if you can tell me where I am wrong.
I am a lousy teacher for those that don't want to learn. I'm a lousy teacher for those that are defiant. For those that are curious and open-minded, even if highly skeptical, I believe I'm a better than fair teacher. Although my record on the internet is a damn sight poorer than my hands-on record. I can't say if that is related to the medium or the audience.
I would have to direct you to exactly 1100 posts.
Subduction Zone
Muse
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See, I was right humber. Seriously , I am sorry spork, any teacher that could put teach humber should definitely be nominated for sainthood.
It is not about you, Spork. You made it that way. I don't mind a bun-fight, so I admit that I like to respond in kind.
You could try defending your ideas, rather than you, or attacking me.
Same goes for you SZ. If I am wrong, you can tell me where I am wrong.
It is solid though. I have though it through. Despite what you may think, I understand very well how you believe it works. It is just that it doesn't actually work that way.
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I do notice Humber has stopped commenting on the balloon that, magically, is at once pushed by wind from behind, yet leaves a bow-wave as it passes "Through" the air to the front.
I'd suspect that shutting up and ignoring is as close as Humber would get to admitting error.
I'd suspect that shutting up and ignoring is as close as Humber would get to admitting error.
Christian Klippel
Master Poster
Hello RossFW,
not quite. If his errors are constantly pointed out to him, he reacts with "threats" of fast-scrolling.
Greetings,
Chris
Humber, that is where you are wrong. You don't understand that it is capable of doing exactly what Drela says it can do, which is to go DDWFTTW, steady state. You don't understand that the treadmill test is a valid proof of that, as stated by Drela et al.
It's that simple. That's what people have been trying to help you with for dozens of pages, but you seem to enjoy the repartee so much that you'll never get to the meat of the topic and actually learn where you are wrong.
I'd like to say that as a teacher, spork is very competent and amazingly patient when people are actually trying to understand, especially considering the amount of fallacious falderal that he has waded through regarding this impractical but intriguing device. He took the time to bring me up to speed on the basics of aerodynamics so I could comprehend the subtleties involved. I argued from ignorance but from a different point of view: I accepted the cart but not his explanation because I knew next to nothing about sailing. Once that was resolved, I've only needed the occasional course correction.
There are a lot of other people on this forum who also understand this and are very helpful, more and in a higher percentage than any other forum I've been to. I truly hope that you too will eventually come to understand how the cart works, not because the cart itself is a big deal but because of the "eureka" moment. It's worth the effort to try, humber.
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Maybe, Mender. I have read his paper, but not yet the power part, but I think that he is taking some liberties. But that is not the point. You can see that it is treated as an engineering problem. A few equations and some estimated factors. There is no equivalency as such. The text does say "ground power" but that is it. The rest is simply the differential velocity of the wind over the ground, as I expect.
The treadmill supports other notions, that are not in Dela's ideas.
That works both ways. It takes effort.
Can't agree with that. If you agree with him, yes, otherwise you are dismissed. Skeptics are not all alike. Some just say "can't work" just because they think so. They are useless, Mark boing-boing included.
Yes, Mender. Nobody gets abuse from me as first strike. Some not at all. That is not the point. The treadmill is wrong. The cart is the cart. It's a propeller and wheels. An entirely conventional engineering problem.
I never "misunderstood" any of the ideas. The "eureka" moment, is the time that you abandon what you have learned, to be transported back 400 years.
You have to agree, that if it is equivalent, then it should pass all the tests, from any "frame". They are inconsistent. It is internally inconsistent. Behavior when fixed to the belt, is not the same as when at windspeed.
Test are difficult, because it cannot support them. All failures result in motion back with belt. It has no valid intermediate states. It cannot be shown to move from belt speed to windspeed, nor any state in between. Only "windspeed"
How so?
No, I am right about that, but it is not what you think it to be.
There is never any real wind on the treadmill, nor is there an effective equivalent. The cart is said to be at windspeed, when stationary w.r.t the belt. That is all.
The assumption is that if "time or belt were long enough" the cart could achieve that state from the initial condition of moving back with the belt.
The differential velocity of the said "wind", drives the cart froward ( via the propellor/wheels) until that windspeed, zero-force state is achieved.
This process is in mimicry of some real objects, in real wind. Balloons can come close to that but never actually do that. Not exactly.
I am not actually interested in that, per se, but this is a notion that supports that process on the treadmill. The process is like a balloon accelerating to windspeed, but only superficially.
That real acceleration cannot be seen on the treadmill, because it cannot do that. If it were not for the way the cart works, as a balance, that limitation would be immediately obvious, and this thread would not exist.
Sometimes, on mud flats during wind and rain. Large rocks are blown by the wind. Like the balloon, they present a large area to the wind, so you would say they get a big push because of that. That is largely correct.
The acceleration is due to that force and the mass, but the final velocity is determined by that driving force, and the opposing drag of the mud.
They do not reach windspeed, ever.
The same goes for water and wind borne objects, because drag is never zero, either pushing or retarding the object.
This argument was about showing the difference between real objects and the treadmill. In reality, all object do not reach windspeed, but are likely to on the belt, if the friction is low enough, or it has some other mechanism, like the orange. That is what "windspeed" is, and nothing more.
Perhaps you not agree. At treadmill windspeed, what force is upon the cart?
Only the drag of the belt. That is the result of friction to the belt, and the force of gravity. Not related to wind load at all.
The reacting force to this is not so much the propeller, but the effect of the cart being dragged back, not against a "wind", but the mass load of the air.
The balance mechanism operates to sustain this state.
Yes, but we are talking about balloons which are entierly within the airmass. What is it that provides drag in opposition to the direction of the wind if they are not even AT the velocity of the wind?
You just don't get the word relative, do you!
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That's the truth! This is a sharper and more open minded group than I've found on any forum. My own interests have been in R/C helis, hang gliding, and kitesurfing primarily. I've discussed this problem on those forums. However, since JB and I posted the videos, this thing has kind of exploded and people have been pointing me to forums and blogs left and right.
Each forum seems to have its own character, and it's own crowd. Perhaps the worst would be the physics forum - where no one seems to understand even the most basic principles of physics - and they just keep locking threads if you talk about witchcraft like DDWFTTW carts.
Personally, I think the cart is really cool because it's such a spectacular brainteaser, and because it leads down an astonishing number of paths of learning for such an incredibly simple device. JB and I have talked for so many hours about the physics, aero, and mechanics of this silly thing. It's also lead us to examine the exact parallels between props and sails and helped us learn some things I certainly never expected about the aerodynamics of sailing (which I thought I had a perfectly good grasp on to begin with).
This problem is also an interesting one in that it seems to have no prejudice. I've seen PhD's in aero and physics, even professors, stubbornly go humber on me, and I've seen people we almost no formal education, but true curiousity come to understand the intricacies incredibly thoroughly.
The cart itself is nothing - but the discussions and learning (and exposing) it provokes has amazed me.
We've also met some incredibly intelligent and interesting people as a result of these discussions.
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There's a world of difference between a skeptic and an A-hole. I've always welcomed sceptics. Frankly I have little interest in talking about the performance curves with people that already understand this thing.
Mark F. may be a sceptic, but he's an open-minded one. Mark requested a kit from me, and will be testing this himself. He asked all the others that got kits to report on their findings as well. Mark will be up this way this month and has asked to get together. He also has communicated with Adam Savage by email suggesting they do a segment on this thing. And he plans to see Adam when he's up this way and remind him.
Useless!? Far from it. I have almost no doubt Mark will publish a follow-up to the original article that appeare in Make magazine. I just hope he'll allow me to write that article.
I suspect humber may actually believe that.
And it does. Including all those tests you say it won't - but fail to disclose to us.
Did that mean something when it was still in your head?
The flow of the medium over the object, creates a wake ahead of the object. This is certainly so when held in a flow. That force is 'drag' for the object when it moves through the medium. It rises faster than the drive force, because it is so often turbulent, and is always there to some degree, for all objects.
That impedance is larger for some objects than others, so the final velocity is different. Almost all objects will be worse than a balloon.
The meteorological balloon is a good example. That equation does not prove that all objects will approach or reach windspeed. However, they do.
The equation, where (V-Vb) is non zero, approximates the difference between the force that is derived from the wind by the object, and that against it. It is a simplified equation. That's point one.
The author then makes that difference zero on the a priori knowledge, that balloons are known to travel close to the wind. That is historically so.
The remainder is just a proof that the balloon can accelerate to the limit of its velocity within the desired time. That is the case for this type of object, specifically, tracking balloons.
The misreading, is used to support other mathematical howlers, to show that all objects reach windspeed, on the a priori assumption that they do !
That equation is valid only for objects that behave like weather balloons, a quite special case. You are arguing from the special, to the general.
Drela uses two primary equations. (21) and (22). Still a simplification, though.
They are the forces of drive and reaction, seen as separate equations.
That has nothing to do with the matter, RossFW.
I dis-agree Spork- The cart isn't nothing. It's a working model demonstrating a very interesting scientific principle.
I jumped on it at first, but reading the explanations and comparing them with my own experiences (ALSO R/C models! Plus I'm a professional pilot, ex-skydiver, glider pilot, sailor and I'm taking my new Blokart land-yacht out for the first time today!!) led me to realize that utilizing relative movement of media (OH!! There's that pesky "Relative" word again!!) was in play.
It's led to a very illuminating and educational thread. In pointing out Humbers errors, we've discussed a lot of interesting concepts, clearly enough to be understood by every one except him!!!
Here's one for Humber- the current R/C model speed record is around 300kph. It was set with a glider utilizing nothing more than the difference in speed between two air streams (what is known as Dynamic Soaring), a free stream of about 50kph and a slower of about 20 in the lee of a hill.
Possible in the Humberverse??
I jumped on it at first, but reading the explanations and comparing them with my own experiences (ALSO R/C models! Plus I'm a professional pilot, ex-skydiver, glider pilot, sailor and I'm taking my new Blokart land-yacht out for the first time today!!) led me to realize that utilizing relative movement of media (OH!! There's that pesky "Relative" word again!!) was in play.
It's led to a very illuminating and educational thread. In pointing out Humbers errors, we've discussed a lot of interesting concepts, clearly enough to be understood by every one except him!!!
Here's one for Humber- the current R/C model speed record is around 300kph. It was set with a glider utilizing nothing more than the difference in speed between two air streams (what is known as Dynamic Soaring), a free stream of about 50kph and a slower of about 20 in the lee of a hill.
Possible in the Humberverse??
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