Dan O.
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Right you are. It seems to match a function of the form v=v0/(kt+1). Just looked like an exponential decay at first glance.
Split Thread The validity of classical physics (split from: DWFTTW)
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Right you are. It seems to match a function of the form v=v0/(kt+1). Just looked like an exponential decay at first glance.
No ambiguity. I am not deceiving you. I like magic because it shows how lame we are at observing, and how often we come to the wrong conclusions, even in general.
Understood. I have never knowingly mislead anyone on this forum, here or elsewhere.
No. Some of what Sol_invictus has said about EM and momentum may have a point. I remember seeing something like this before, regarding TEM waves, I think, but that is not of direct consequence to the treadmill.
Mixed opinions as to how the cart works, or should work, but that is straight forward engineering.
The treadmill is nonsense. That is not rhetoric. It is stupefyingly wrong.
Extra credibility? Is there a sale on?
There is nothing, Clive, but I am not one for belief.
Well, it is no.
Not directed at you Clive, but "admitting I am wrong" is given pride of place. I find this to be extraordinary.
It's giving yourself a slap on the back for being wrong, while suggesting that not only is the admission call for celebration, but the very improbability of the error itself. Is it possible to be more conceited than that?
So, if I am wrong I will simply tell you. I won't dance on the simple admissions of others.
The question stands. For a 0.1 kg balloon, with a volume of 0.21 cubic meters, a cross-sectional area of 0.427 square meters, and a radius of 0.369 meters, assume a steady wind speed of 1 m/s, a drag coefficient of 0.4, and an air density of 1.293 kg per cubic meter. Release the balloon from its tether. What will the "terminal velocity" of the balloon be? I assert that it is 1 m/s, and in fact that it will reach a speed of 0.9995 m/s within 3.2 seconds after being released (somebody check my calculation on that part). As more time elapses, the speed of the balloon will asymptotically approach 1 m/s. Do you think the number will be different? Either calculate it, or tell us what additional information you need, or tell me how to do the calculation. The problem that I have with figuring out what the speed is in the humberverse is that as far as I can tell, there are two different airspeeds that the balloon experiences simultaneously, one being a headwind and the other a tailwind, and I have no idea what they would be.
Mark Drela claims the treadmill is not wrong. So on one side we have:
- Everyone but humber on this forum
- Chapter 1 of Intro to Highschool physics
- Mark Drela (PhD in Aero, MIT professor of Aero, and one of the best minds in Aero today).
And on the other side we have:
- humber
Yeah - I suppose this would come down to a coin toss.
Not quite. Reference for Mark Drela personally giving support for you treadmill.
Are you going to admit you're wrong if I produce that evidence?
Hell, Mark Drela could personally come to your home, show you three forms of government issued picture I.D., tell you the treadmill test as demonstrated by JB and spork is absolutely representative of an outdoor downwind test, re-tell the whole story through interpretive dance, and finally sign documents to that effect, and have them notarized - and you'd tell us "that's not what he meant".
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I'll let you attack the argument before I provide evidence that it comes from Mark Drela. No point in bringing matter and anti-matter together if I don't need to after all.
So here's how it goes...
Critic says:
Drela responds:
So it seems (to all other sentient beings) that he also laid to rest your notion that a hot air balloon doesn't drift at wind speed. Although I realize it won't seem that way to you.
So here's how it goes...
Critic says:
Drela responds:
So it seems (to all other sentient beings) that he also laid to rest your notion that a hot air balloon doesn't drift at wind speed. Although I realize it won't seem that way to you.
No need, there is a similar example given in the text. The formula is an approximation based upon the simplification that (V-Vb)^2, can be V-Vb. There is no doubt that some objects can get close to the wind, bubbles being one example, but not reach it. In this case, the drag that the bubble sees ahead of it is so low, that is can get close to windspeed before that drag, exceeds the force available to it. Unless you can make that zero, and so contradict Newton, the bubble will not reach windspeed.
The author simply ignores this limitation, because he says "they usually follow the wind flow". He uses that assumption to show that it will track variation, because the accerleration is acceptable, but the mean speed will vary according to circumstance, including the frequency and distribution of gusts, and the 'crest factor' the ratio of mean to peak winds. The definition of 'mean' is quite wide, nd perhaps not the one you are assuming to be so.
You don't get an entire course of the nature of bacteriological balloons on one page, jjcote.
Of course, if you are correct, you should also be able to show that all objects can do the same, not just a special example of something that is like air. I said this before, with the 'water canoe'. The more it is 'like' water, the closer it will approach waterspeed. Balloons are close, bubbles closer, but not at all most objects, including sails and windcarts.
I repeat my question: if the "terminal velocity" of the balloon is not 1 m/s, then either tell us what it is, or tell us what additional information is needed to calculate it. You have clearly stated that the propulsion from the wind will balance out with the drag at some speed. What is that speed?
Hey spork, did you tell Mark that I said "hi"?
John Freestone
Graduate Poster
Parsing humber
Then some more clarity about the treadmill. What most people would consider beliefs. Yet humber is "not one for beliefs", he says. What does that mean, not to be "one for beliefs", yet unrhetorically state that something is stupefyingly wrong and nonsense? Does it mean that it is an absolute fact, which humber can discern like an absolute velocity? Does he mean that he doesn't bother with beliefs because he knows; mere mortals deal in beliefs? We might construe that, but who knows when what has been said is so ambiguous?
What about this then:
But before we get to that - the whole thing started with an aside, "Not directed at you Clive, but". So, depending on whether humber thinks owning up to stuff is a good or a bad thing (I'm not sure now), he may or may not be saying that Clive does or doesn't do that and he doesn't hold it against him, and in the process insinuating that someone else may...or may not...and he does. Clear so far? Maybe the following will shed some light.
It also, curiously, seems to suggest to him that when we say we were wrong we express the conceit that it doesn't happen very often. Perhaps the more we say we were wrong, then, the more arrogant we show ourselves to be, and by stating so clearly (if qualified a little) that he was never wrong about anything here in this thread, humber is obviously being humble. Humble people don't slap themselves on the back for being wrong every ten minutes, after all! (Oh, I know, you hawk-eyed people, I've edited out the bits where he said there were things he learned about something-or-other - VEM or PIM or I don't know what - but that had nothing to do with anything anyway; let's forget that shall we?)
Is that what he means, then, that saying you were wrong is arrogant? There is hardly any point in asking him. Ah, but there's even more ambiguity to come. Have I just misunderstood the whole tenor of his meaning?...
And, to summarise, just in case we were in any doubt as to his meaning, we get it all wrapped up in a nutshell, final clarity par excellence:
Deep. A koan? Accusative, but vaguely so, and rather superior-sounding.
Are you glad you asked, Clive? If humber was wrong, he'll tell you, unless he's too self-effacing for that.
No ambiguity? Hmmm. Let's see, There are mixed opinions as to how the cart works. Humber's mixed opinions? Or mixed opinions on the forum generally? Ah, it must be others who have mixed opinions, because "that is straight forward engineering". Clear enough about that. If there were mixed opinions, they were someone else's.
Then some more clarity about the treadmill. What most people would consider beliefs. Yet humber is "not one for beliefs", he says. What does that mean, not to be "one for beliefs", yet unrhetorically state that something is stupefyingly wrong and nonsense? Does it mean that it is an absolute fact, which humber can discern like an absolute velocity? Does he mean that he doesn't bother with beliefs because he knows; mere mortals deal in beliefs? We might construe that, but who knows when what has been said is so ambiguous?
What about this then:
The first sentence is ambiguous immediately for not having a subject. Someone, we must assume, gives pride of place to the act of admitting they were wrong, but we're not told who that is. It might mean humber, if we choose to read it that way: he could be affirming his habit of saying when he's been wrong about something. That would add weight to his firm (absolutely unqualified) "No" to whether he was wrong about anything. On the other hand, it could be a criticism of how others hold such openness in high esteem, or a mere observation that they do. He finds it extraordinary, which suggests that perhaps the criticism of others is a more correct reading, as do some of the following.
But before we get to that - the whole thing started with an aside, "Not directed at you Clive, but". So, depending on whether humber thinks owning up to stuff is a good or a bad thing (I'm not sure now), he may or may not be saying that Clive does or doesn't do that and he doesn't hold it against him, and in the process insinuating that someone else may...or may not...and he does. Clear so far? Maybe the following will shed some light.
Yes, no, I mean, now it begins to appear that what is commonly considered a virtue humber sees as a vice. Admitting a mistake, saying sorry, giving way in an argument, seems to indicate to humber a self-aggrandisement, 'a slap on the back for being wrong' and 'cause for celebration'!
It also, curiously, seems to suggest to him that when we say we were wrong we express the conceit that it doesn't happen very often. Perhaps the more we say we were wrong, then, the more arrogant we show ourselves to be, and by stating so clearly (if qualified a little) that he was never wrong about anything here in this thread, humber is obviously being humble. Humble people don't slap themselves on the back for being wrong every ten minutes, after all! (Oh, I know, you hawk-eyed people, I've edited out the bits where he said there were things he learned about something-or-other - VEM or PIM or I don't know what - but that had nothing to do with anything anyway; let's forget that shall we?)
Is that what he means, then, that saying you were wrong is arrogant? There is hardly any point in asking him. Ah, but there's even more ambiguity to come. Have I just misunderstood the whole tenor of his meaning?...
If he's wrong, he'll simply tell us!? He must think it's good to own up to it when you're wrong. That's what I thought several paragraphs ago. I was wrong. And then I was wrong again. My God! How conceited of me! He's expressed it so clearly. He will simply tell us if he's wrong.
And, to summarise, just in case we were in any doubt as to his meaning, we get it all wrapped up in a nutshell, final clarity par excellence:
Oh.
Deep. A koan? Accusative, but vaguely so, and rather superior-sounding.
Are you glad you asked, Clive? If humber was wrong, he'll tell you, unless he's too self-effacing for that.
Spork was right, no sense casting pearls before swine.
Regarding humber's post about Mark Drela's response to spork's question: humber, that is one of the most self-serving purposely misinterpreted pile of garbage that you've spouted so far. You absolutely have no desire to learn. It is manifestly evident that you can't let go of your flawed understanding. At one point I thought it was possible to help you past this, but it can't happen until you can accept that you are wrong.
Regarding humber's post about Mark Drela's response to spork's question: humber, that is one of the most self-serving purposely misinterpreted pile of garbage that you've spouted so far. You absolutely have no desire to learn. It is manifestly evident that you can't let go of your flawed understanding. At one point I thought it was possible to help you past this, but it can't happen until you can accept that you are wrong.
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No, no, no.
The book is an introductory text to meteorological measurement.
In this case, the author is not concerned with the terminal velocity, but the ability to track the wind, against the mean flow (an indeterminate quantity).To simplify the equation, the force is assumed to be a linearly related to the difference in velocity of balloon and wind. It is not necessary that the balloon be even close to windspeed to display the variation.
It can travel slower. What they are NOT looking for is a balloon that "stays at zero velocity w.r.t the wind" because then, the result would be constant!
The balloon must let the wind "pass by it" or it would be held in a pocket of air traveling at the same velocity.
The author makes a simplifying assumption, then test his calculation ( not empirical measurement!) against a slow wind. Why?
To show that the variation is linear, that is a linear indicator of the difference of speed over a wide range of mean speeds. The indication will not be compressed by the absolute speed.
The speed of a natural fluid is vexed. If you place a hydrometer in a river, you will get variations across the river, as well as up or downstream.
To resolve this, dyes are used, because they behave "just like water" and the average journey time is used to compute the mean velocity.
Different objects in water, behave differently. If the river is glass like, I suppose a water beetle held by surface tension, will travel at the surface speed of the water. Some objects behave like Rayliegh says, some like Stokes, and others in a class where boundary conditions dominate.
If not, I would ask you to explain why some river borne sediments settle to the river bed according to their size, whereas very fine sediments travel to the sea?
If an object is dragged through oil, it generates a drag proportional to the square of the velocity. So, it is a parabola, passing through the origin. Let's say that at 10m/s that force is 20N. Now, I think you will agree that this is the same force, that the same object will experience, if held in a flow of the same oil at 10m/s?
If released, you say that the object will be accelerated in a manner that is the reverse of the dragged situation, so as to arrive at the origin (0,0) of the force parabola. Zero force.
No. The situations are no symmetrical. The force in the dragged case is external, unlimited, and directly coupled to the object. In the oil, the object gets its force not directly, but via drag. The object is not oil, so that makes the situation asymmetrical.
If the force on the object is the square of the difference, then it will be accelerated by a rapidly decreasing force. Ahead of the object, there will be the opposing force of drag. Now, this is turbulent, and not laminar, it is the wake of the fluid over the object. This force rises much faster than the applied force, so the object never reaches oilspeed.
Want a solution? Find a good CFD programme.
Subduction Zone
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Now in the humberverse we find that fluids need to take Valium: "The speed of a natural fluid is vexed"
I don't have any humber quotes yet, but this one ranks right up there
I don't have any humber quotes yet, but this one ranks right up thereDan O.
Banned
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http://journals.cambridge.org/actio...487EC4E690.tomcat1?fromPage=online&aid=367122
be sure to look fro the update that gives a non-intuitive correction
be sure to look fro the update that gives a non-intuitive correction
You have got to be kidding, Mender. One of my major criticisms of the treadmill is that it treats wind as a 'velocity'. I have repeatedly said that the is not a velocity, but a "moving mass". That is how Drela see's it, too.
That is what is missing from the treadmill. Every critic has said the same "there's no wind".
Yes, don't forget that he says "watermass" and included ground power as a misconception, or that the remarks are about the real world, and not treadmills. Other than that, a pearl.
Brian-M
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You just noticed that?
No... I just have to remind myself of it from time to time.
I remember one time as a kid I was staying with a cousin with an old Commodore 64. After loading up one of the programs a sentence appeared, and whenever I pressed a button, it would be replaced by another.
At first, I was wondering what it was talking about, as I tried to find a connection between the statements. It took a couple more sentences before I realised the program was generating sentences by applying grammatical rules to randomly selected words.
Humber seems a bit like that... sometimes you can forget he's just spouting random gibberish.
Yep, saw that. It was one of the 'special classes' I referred to. In this case, I think the author is arguing that the surface tension allows the objects to travel faster than other layers.
Other objects that are not boats are water beetles, tracking dyes and sediment.
Noteworthy is the fact that the channel is at an angle, so perhaps gravity may have something to do with it.
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