Split Thread The validity of classical physics (split from: DWFTTW)

[jjcote]

No, no, no. (...blah blah blah...)
Want a solution? Find a good CFD programme.

Um... does this mean that you don't know how to calculate the terminal velocity of the balloon? I don't care what the guy in the meteorology book was trying to do (although I'm completely aware of what he was doing, and you evidently aren't), I just want to use the numbers in his example to ask a simple question.

In a constant 1 m/s wind, what will the "terminal velocity" of that balloon be? Or do you need additional information?

 

[Reality Check]

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.

hummer, you are aware that rivers run downhill, i.e. at an angle?

 

[Brian-M]

Motion of the canoe through the water generates drag ahead of the canoe, and that opposes the motion of the canoe.

If the canoe is travelling at the speed of the water, it is travelling with the water, not through it. If the canoe is not travelling through the water, there isn't any drag.

Drag opposes motion of an object relative to the medium causing the drag.

If the canoe is travelling slower than the water, then relative to the water the canoe is travelling backwards. The drag from the water will oppose this backward motion by accellerating the canoe until the canoe is travelling at the same speed as the water.

The only possible reason a free-floating canoe wouldn't reach water-speed is if air-drag on the above-water parts of the canoe has a measurable effect, and in most cases this would most likely be negligable.

 

[humber]

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.

Hello, Brian_M. That must be in reference to the double speed cart. Do you think Micheal_C's demonstrations is convincing?
Did you notice in the first video, where the sheet of paper beneath the cart wheels is the equivalent of table in one case, and then the motion between the paper and the driving ruler is actually the differeence betwen the left and right hands of the operator, both with a common force return to ground (table)?
Yet, when the propellor is introduced, one of the 'hands' is no longer available? If the paper slips under the wheels, why doesn't it do so when the cart is pushed by hand?

 

[humber]

hummer, you are aware that rivers run downhill, i.e. at an angle?

When water runs down hill, it accelerates and so acquires more energy. That is not the case with constant velocity flow.
ETA:
Sometimes rivers run uphill. Momentum carrying it forward over a rise. for example.
All that is required is that the average be down hill.

 

[mender]

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.

You are so caught up in your weird interpretation that everything you read appears to be supporting your belief system. Read it again - or not, you failed miserably to understand what he said the first time, why should the second time be any different?

And your reason for saying the wind is a moving mass is only so that you can include your faulty understanding of KE and work in yet another bizarre display of "logic". You refute any other references to using the air mass as something that can be used as part of a gearing system, which is how the prop cart manages to travel directly downwind faster than the wind steady state - but that is a different thread.

This one is supposed to be about your lack of understanding about frames of reference, not your lack of understanding about how the prop cart works or what is happening on the treadmill, even though it is extremely obvious that you are always checking your answers against your preconceived notion that DDWFTTW travel is impossible.

 

[humber]

Couldn't have said it any better, spork. And humber still doesn't see it. Can't see, won't see, even if Drela told him to his face exactly what he is saying and meaning.

Yes, you can see quite clearly that Drela tells Spork to his face that he agrees that the treadmill is a valid model of a cart at windpeed, even though the unknown author's question specifically excludes "multiple HP treadmill power"


'

 

[Brian-M]

The book quite clearly states that the balloon travels at the mean speed of the wind. The concern is that the dynamic behaviour of the balloon will not allow it to track the variations around that mean windspeed.

(1) If the balloon spends any time accelerating, its average velocity must be below that of the wind. Intermittent changes in the wind's peak velocity are used to accelerate the balloon from its lower mean value, so that the changes may be tracked.

Humber... if there are variations in wind speed, then the wind itself is accelerating, so anything that tracks wind speed must also accelerate in order to accurately track it.

It may be true that the balloon won't accelerate as fast as the wind does... but the balloon won't decelerate as fast as the does either, so while at times the balloon will be moving slower than the wind, at other times it will be travelling faster than the wind.

The end result is the average speed of the balloon will be the same as the average speed of the wind... in other words: windspeed.


Perhaps you fail to understand the definition of mean?

The arithmetic mean is the "standard" average, often simply called the "mean".

So, mean is synonymous with average, and the mean speed of the wind is what most people call "windspeed".

The mean speed of the wind is windspeed.

And you're telling us that the balloon doesn't travel at windspeed, because it's only going at the mean speed of the wind?


EDIT: Ah, Sol beat me to it.

 

[Subduction Zone]

One more question for humber. humber it you jumped at a high altitude, say 20,000 feet, would you fall at, faster, or slower than your terminal velocity? And why?

 

[spork]

spork brilliantly and against all odds predicted the future as follows:

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".

So now we have Mark Drela on one side (with his PhD in Aero, prof. of Aero at M.I.T. and generally thought to be one of the sharpest aero minds in the field), and on the other we have humber (a guy who can't construct one sentence without changing his mind twice midstream).

If anyone for a moment thought there was some hope of putting humber on the right course - I hope this puts that to bed for you.

humber is to be used for entertainment purposes only. Any other use is not covered by warranty.

 

[spork]

Hot air balloons have an engine Spork, yes heat is an engine. Hot air ballons use altitude, and ride thermals. They have an operator who controls the engine...

This is brilliant. I've been flying hang gliders and sailplanes for almost 15 years now. When I want to ride a thermal I have to first FIND the thermal. 99% of the time this requires me to move relative to the air mass I happen to be in. Then if I want to make use of that thermal I have to dwell in it. I fly slower in lift than I do in sink (yes - if there's lift there's also sink), and I circle in that lift while I speed through the sink in relatively straight lines. I can't wait to hear how the balloon "operator" manages this!

Hopefully humb will take a crack at this one too. I'm going to dial 9-1 and keep my finger over the 1 when I read the response. Whether we get humb or humber I'm likely to die of laughter either way.

Yes, you can see quite clearly that Drela tells Spork to his face that he agrees that the treadmill is a valid model of a cart at windpeed, even though the unknown author's question specifically excludes "multiple HP treadmill power"

For the record:

1) I honestly can't follow that sentence, but I'm sure it says something wrong.
2) I've never been face to face with Mark Drela, and I didn't pose the question. I did enjoy the fact that he just happened to dispose of both of humber's claims (balloons that can't keep up with the wind and carts that can tell the difference between inertial frames) all in one go.

One more question for humber. humber it you jumped at a high altitude, say 20,000 feet, would you fall at, faster, or slower than your terminal velocity? And why?

HEY! That's two questions. And besides, you're just poking at the side show freak now. You're clearly just giving him fuel to entertain us. Why else would you ever think to ask him a question more subtle than "what does 2+2 equal?".


In fact I'm going to make a point here. And this is in all seriousness. humber - I claim 2 + 2 = 4. What do you think of that?

 

[Brian-M]

The balloon must let the wind "pass by it" or it would be held in a pocket of air traveling at the same velocity.

YES! When it's travelling at wind speed you could think of it (in a way) of being held in a "pocket" of air travelling at the same velocity... except that this "pocket" constitutes the entire body of air.

If the balloon is travelling at less than windspeed, then the air pushes the balloon to a faster speed as the air passes by. As such, the balloon cannot remain below windspeed because the wind keeps pushing it faster.

However, if it is travelling at windspeed it can remain at that speed indefinetly, because the wind is no longer exerting a net force on it, and objects in motion tend to remain in motion unless acted upon by an outside force.

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".

"Wind" is the relative motion of the air. The air is moving relative to the surface of the treadmill (which is acting as the ground).

If wind is the relative motion of the air, and the air has motion relative to the surface treadmill, then for something on the treadmill, there is wind.

Every critic of the treadmill test forgets this.

 

[spork]

If wind is the relative motion of the air, and the air has motion relative to the surface treadmill, then for something on the treadmill, there is wind.

Every critic of the treadmill test forgets this.

Including professors of Physics, Aero, and M.E. (yes I can name one of each - and I'm sure there are MANY more). It makes me want to cry.

I didn't just post Drela's post to this list. I also emailed it to a professor that swears the treadmill and the wind over a road are unrelated. This seems brutally obvious to me. But I hoped maybe this guy would budge from his humber-like position if he heard it from another PhD. I'm making myself sad just typing this.

 

[RossFW]

Hot air balloons have an engine Spork, yes heat is an engine.

Which they use to alter the density of the air in the envelope in order to provide buoyancy and for no other purpose. It in no way provides thrust for lateral movement. Hydrogen balloons do NOT have an engine, and move at the speed of the wind, as do hot air balloons.

Hot air balloons use altitude, and ride thermals.

No, they don't. They work just fine in still (lateral AND vertical) air.

 

[Subduction Zone]

Including professors of Physics, Aero, and M.E. (yes I can name one of each - and I'm sure there are MANY more). It makes me want to cry.

I didn't just post Drela's post to this list. I also emailed it to a professor that swears the treadmill and the wind over a road are unrelated. This seems brutally obvious to me. But I hoped maybe this guy would budge from his humber-like position if he heard it from another PhD. I'm making myself sad just typing this.

Right now I am having fun arguing with GMB (gumber?), someone who does not believe in the special theory of relativity. There may be a connection between the treadmill not being a valid frame of reference and Einstein being all wet, I will keep you informed. I fear that if GMB and humber got together we might have the first internet singularity. The whole internet could disappear in a black hole of ignorance and arrogance.

 

[humb]

This is brilliant. I've been flying hang gliders and sailplanes for almost 15 years now. When I want to ride a thermal I have to first FIND the thermal. 99% of the time this requires me to move relative to the air mass I happen to be in. Then if I want to make use of that thermal I have to dwell in it. I fly slower in lift than I do in sink (yes - if there's lift there's also sink), and I circle in that lift while I speed through the sink in relatively straight lines. I can't wait to hear how the balloon "operator" manages this!

Hopefully humb will take a crack at this one too. I'm going to dial 9-1 and keep my finger over the 1 when I read the response. Whether we get humb or humber I'm likely to die of laughter either way.

Happy to oblige, you ridiculous foon! A hot-air balloon can ride thermals just as your hand glider does, but can also create internal thermals via its heat engine. It rises due to the density principle (the same technique that allows one to trivially sort out mixed salt and pepper), and can go wherever it wants by descending and turning the potential energy into kinetic energy. The energy has to go somewhere, and it can't turn into heat, or the balloon would go up again, so it must become velocity. The direction is determined by which way the passengers in the basket lean. This is common knowledge. It is the same principle that you use when flailing your legs about in an attempt to steer your hand glider. By the way, you would do much better to fly faster in lift, because the wing provides a greater lifting force at higher speeds and you should take advantage of that when you are already going up. You need to fly slowly in sinking air currents, however, so that the air molecules won't notice you. You would also do well to use a basket with your hand glider, as balloonists do, so that your arms won't get so tired from holding on. This has been understood for a millennium!

In fact I'm going to make a point here. And this is in all seriousness. humber - I claim 2 + 2 = 4. What do you think of that?

In Euclidean or Lobachevskian space? I see where you are going with this, and I won't be a victim of that sort of sophistry, either!

 

[spork]

I swear - you got me again you rat-b@st@rd. I was getting ready to start replying before I realized you were missing the "er".

Happy to oblige, you ridiculous foon! A hot-air balloon can ride thermals just as your hand glider does,... This has been understood for a millennium

Nicely done!

 

[RossFW]

Oops!!

 

[Thabiguy]

Right now I am having fun arguing with GMB (gumber?), someone who does not believe in the special theory of relativity. There may be a connection between the treadmill not being a valid frame of reference and Einstein being all wet, I will keep you informed. I fear that if GMB and humber got together we might have the first internet singularity. The whole internet could disappear in a black hole of ignorance and arrogance.

I see a difference there. I think humber has been able to stay relatively polite through all this. I mean, sure, there is an occasional nip here and there, but it's nothing like the vitriolic, burning bile that GMB has been spewing.

 

[Clive]

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.

Thanks for your response humber. I like magic also. I don't think you are deceiving me any longer but I'll watch the show anyway!

I have never knowingly mislead anyone on this forum, here or elsewhere.

I hear you...

Mixed opinions as to how the cart works, or should work, but that is straight forward engineering.

My interpretation of this sentence is that you are not speaking for others, and that therefore the "mixed opinions" are yours.

The treadmill is nonsense. That is not rhetoric. It is stupefyingly wrong.

I've never seen any explanation that I could properly understand for why you have such strong views on the treadmill. I think this applies to other people also. If you wish to convince us, then I really think you need to detail your views on this again in a complete and unambiguous way, possibly even including the basic principles and assumptions you are working with if there seems to be any possibility of confusion in that regard.

You've also indicated that my scenario (#2744!) of essentially using half the world as a large treadmill is somehow wrong but have chosen not to explain why. I also don't think you ever really replied properly to JJcote about his scenario of the cart being tested on an aircraft carrier in the fog - maybe that one ran aground. You didn't think that having the treadmill running on a moving truck in a real wind made any difference when it comes to the validity of using a treadmill. So what exactly is the common issue you've identified with all these scenarios (and others that I may have missed)? In other words, what has to be "removed" or "added" to make any or all of these scenarios acceptable to you? Or are you saying they all have different problems?

Well, it is no.

That is clear. In other words, you are saying that for all intents and purposes, essentially nothing that anybody has written or presented to you in any other way so far has led you to make any change to the way you understand "physics" (in the context of the relevant threads in these forums).

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?

Like John earlier, I couldn't quite work out what you were trying to convey in this part of your response. You have already confirmed that as far as you are concerned, nothing presented to you so far in these threads has exposed any errors in your knowledge or understanding of the relevant physics. You are entitled to that view obviously. However, given that I am also sure you are wrong with your complete rejection that a cart on a treadmill in still air can validly be used as substitute for the cart rolling downwind on the ground at around wind speed, I am left struggling to understand your viewpoint. If however, you had admitted to finding some area of your knowledge and understanding was in fact wrong to start with, and that you'd had to change your views in that respect, then I think I would have felt that there was a little more hope of somehow breaking the impasse. So I'm simply trying to get a handle on how confident you are about your knowledge and views, how open you might be to the possibility of seeing things a different way, and so on. At best, all very subjective though!