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  #31 (permalink)  
Old 18-July-2007, 05:17 PM
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Originally Posted by tusenfem View Post
The speeding up of the flow has completely nothing to do with Bernouilli's law (which states that the pressure perpendicular to a flow becomes less,
When its Speed is Increased.
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...see the experiment with two sheets of paper and blowing in between them and have them move together), but has all to do with the continuity equation that I described above.
And you can't see any paradox? You blow between the pages - and they move together. Wouldn't one expect them to move apart? And 'paradoxically' they move together?

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Naturally, at the begining there will be a slowing down of the flow, which gets transported upstream by (shock)waves. After the steady state has set in, th continuity equation demands that in the narrow the flow speeds up, otherwise the river will overflow at the narrow part.
I have to thank you for these continuity equations and the knowledge you bring. This helps everybody. Greatly.

But did you imagine I didn't know this?

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And the last part does not really make sense the way it is written, because it seems to imply that you expect it to slow down,
Not me, not now - but I'm thinking of when I was a child - I think I would have expected the river to slow down at the restriction. I'm not ashamed of that.

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but you think that Bernouilli says (dunno why you think that he says that) that it should speed up.
Fluid in a tube - water in a river... Is there really no relationship, to you?

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You seem to like the term paradox, but that is mainly because you use the wrong physics.
This Speeding Up Expansion belonging to an Inward movement - or vortex, according to Victor Schauberger. I call it the Penultimate Paradox. I guess there's 'Wrong Physics' just like there's 'Bad Astronomy'.
  #32 (permalink)  
Old 18-July-2007, 05:20 PM
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Well, i'll have to read that again. But incompressible gasses? Which gas can't you compress? Bring it to me - I'll show you how to do it. One way I know is to reduce its volume.
http://en.wikipedia.org/wiki/Fluid_d...pressible_flow

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A fluid problem is called compressible if the pressure variation in the flowfield are large enough to effect substantial changes in the density of the fluid. Flows of liquids with pressure variations much smaller than those required to cause phase change (cavitation), or flows of gases involving speeds much lower than the isentropic sound speed are termed incompressible.
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  #33 (permalink)  
Old 18-July-2007, 05:21 PM
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Originally Posted by Amber Robot View Post
An oxymoron is a phrase that is self-contradictory. The word "expansion" means outward.
Don't you mean "pansion" in an "outward" direction?

Just trying to be precise.
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  #34 (permalink)  
Old 18-July-2007, 05:25 PM
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Originally Posted by thothicabob View Post
I think what ur describing also has to do with as you blow up a balloon, the volume increases so it takes more air to expand the radius of the balloon a given distance, but overall, the volume is increasing at the same rate; it's just spread out more, and the expansion appears to be slower (and it is, radially, but - assuming the amount of air you input remains at a constant rate - the volume increase remains about the same).
Just like I've been saying - this outward expansion slows down. But doesn't every outward expansion?
  #35 (permalink)  
Old 18-July-2007, 05:30 PM
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Well, I guess I stand corrected - once again. Thanks for joining in Kelfazin. I haven't heard from you before.
  #36 (permalink)  
Old 18-July-2007, 05:30 PM
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Just like I've been saying - this outward expansion slows down. But doesn't every outward expansion?
Umm, yeah, if the rate of increase in volume is constant (read my subsequent post trying to explain it more clearly). This is just the mathematical/geometric result that comes from increasing the volume of a sphere at a constant rate; the diameter will increase at a decreasing rate. The same thing happens when you reverse the process; i.e. when the volume of a sphere decreases at a constant rate, the diameter of the sphere decreases at an increasing rate.

I personally see no mystery, unless I am missing something very fundamental somewhere (which, in my case, is always possible, however unlikely it may be).
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  #37 (permalink)  
Old 18-July-2007, 05:35 PM
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Originally Posted by thothicabob View Post
Don't you mean "pansion" in an "outward" direction?
Just trying to be precise.
I like this Inward Expansion, even if it is an oxymoron. You see, the alternative... 'implosion' ... has an opposite - 'explosion'. But I don't see Outward Expansion as, necessarily, an explosion. I mean, the Cosmos is supposed to be Expanding Outwards - but we don't say it is exploding.
  #38 (permalink)  
Old 18-July-2007, 05:39 PM
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Well, I guess I stand corrected - once again. Thanks for joining in Kelfazin. I haven't heard from you before.
Not really joining in, just lurking, I have no position on either side of this debate. Although I had heard about incompressible gasses before and thought I would provide a link.
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I was just sitting here contemplating the immortal words of Socrates who said, "I drank what?"

"Think of the rivers of blood spilled by all those generals and emperors so that, in glory and triumph, they could become the momentary masters of a fraction of a dot." --Carl Sagan "Pale Blue Dot"
  #39 (permalink)  
Old 18-July-2007, 05:44 PM
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Originally Posted by thothicabob View Post
Umm, yeah, if the rate of increase in volume is constant (read my subsequent post trying to explain it more clearly).
I have to go with this one for now.

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This is just the mathematical/geometric result that comes from increasing the volume of a sphere at a constant rate; the diameter will increase at a decreasing rate.
I see.

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The same thing happens when you reverse the process; i.e. when the volume of a sphere decreases at a constant rate, the diameter of the sphere decreases at an increasing rate.
Hey, neat.

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I personally see no mystery, unless I am missing something very fundamental somewhere (which, in my case, is always possible, however unlikely it may be).
No, no mystery - except where can we see an outward expansion that speeds up? The concept defies Nature. Come on, somebody - give me an example of an outward expansion that Speeds Up. Bet you can't - because it doesn't exist. I know lots of examples of Inward Expansions Speeding Up, but only Outward Expansions slow Down and Stop.
  #40 (permalink)  
Old 18-July-2007, 05:48 PM
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In a static system the outward expansion would slow as the volume increases, but what if the system isn't static? What if the energy causing the expansion is increasing?
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I was just sitting here contemplating the immortal words of Socrates who said, "I drank what?"

"Think of the rivers of blood spilled by all those generals and emperors so that, in glory and triumph, they could become the momentary masters of a fraction of a dot." --Carl Sagan "Pale Blue Dot"
  #41 (permalink)  
Old 18-July-2007, 05:49 PM
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Umm...
All this does is to tell me there's something you know that you're not saying. That's okay. If you want, just think it. Maybe it's better this way. Thanks for your input. Sincerely.
  #42 (permalink)  
Old 18-July-2007, 05:52 PM
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Originally Posted by Kelfazin View Post
Not really joining in, just lurking, I have no position on either side of this debate. Although I had heard about incompressible gasses before and thought I would provide a link.
Ok. lurk.

Anything helpful is appreciated. Thanks for straightening me out. But Kelfazin, do you know of an outward expansion that speeds up? Could there be such a thing?
  #43 (permalink)  
Old 18-July-2007, 05:53 PM
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see my other post
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I was just sitting here contemplating the immortal words of Socrates who said, "I drank what?"

"Think of the rivers of blood spilled by all those generals and emperors so that, in glory and triumph, they could become the momentary masters of a fraction of a dot." --Carl Sagan "Pale Blue Dot"
  #44 (permalink)  
Old 18-July-2007, 05:56 PM
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Originally Posted by astrocat View Post
...where can we see an outward expansion that speeds up? The concept defies Nature. Come on, somebody - give me an example of an outward expansion that Speeds Up. Bet you can't - because it doesn't exist. I know lots of examples of Inward Expansions Speeding Up, but only Outward Expansions slow Down and Stop.
Well, apparently the universe's expansion is speeding up now, but...that's a different thing.

It really comes down to the rate at which the volume is increased; if you can somehow manage to keep increasing the rate of volume increase sufficiently, you could maintain an increasing rate of increase in the diameter, too. But the rate of volume increase would have to continue at an ever increasing-rate to maintain that sort of ratio.

I don't know that I have much else to add here (or that I've even added anything at all anyway), but I gave it a shot...!
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  #45 (permalink)  
Old 18-July-2007, 05:57 PM
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In a static system the outward expansion would slow as the volume increases, but what if the system isn't static? What if the energy causing the expansion is increasing?
Now you're getting interesting. Of course, if you add energy - well, my theory breaks down completely. But what if you dont add anything? Does the system still have to be static?
  #46 (permalink)  
Old 18-July-2007, 06:05 PM
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Now you're getting interesting. Of course, if you add energy - well, my theory breaks down completely. But what if you dont add anything? Does the system still have to be static?
Well, that's the thing - you'd have to keep adding energy to have an ever-increasing rate of expansion in terms of size (diameter).

Not 'addiing' anything, I think, implies a static system, or at least a closed one, and in a closed system, you couldn't (by definition) add energy (and (being able) to do so would then make it an open system, not a closed one).
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  #47 (permalink)  
Old 18-July-2007, 06:07 PM
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Well, apparently the universe's expansion is speeding up now, but...that's a different thing.
I'd say it's good as fact.

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It really comes down to the rate at which the volume is increased; if you can somehow manage to keep increasing the rate of volume increase sufficiently, you could maintain an increasing rate of increase in the diameter, too. But the rate of volume increase have to continue at an ever increasing-rate to maintain that sort of ratio.
Adding Energy exponentially would maintain the outward expansion - but where are you going to get all this energy?

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I don't know that I have much else to add here (or that I've even added anything at all anyway), but I gave it a shot...!
Please don't feel that way. Your input has been valuable. Weren't you the first, or one of the first to reply to this thread? Do you think I didn't notice?
  #48 (permalink)  
Old 18-July-2007, 06:10 PM
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Something else to consider while you blow up the balloon: When the balloon is flat, you have to apply a large amount of pressure to begin the inflation. It's hard to get it started. But then once it's started, and before it starts to reach its maximum size, it's a lot easier to cause expansion with less pressure. So right as you cross that line from initial expansion to full expansion, you have an increasing rate of expansion with less expenditure of energy and pressure. Then as the balloon reaches maximum size, you have to increase the pressure to keep the volume going up.

Maybe we can apply this to the expansion of the universe. The BB was the initial, high pressure expansion, now we're in the "middle" low pressure, high expansion state, and in the future we'll hit the high pressure, low expansion state. I dunno.

Do I know how this applies to whatever your position is? Not really. Just a thought
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I was just sitting here contemplating the immortal words of Socrates who said, "I drank what?"

"Think of the rivers of blood spilled by all those generals and emperors so that, in glory and triumph, they could become the momentary masters of a fraction of a dot." --Carl Sagan "Pale Blue Dot"
  #49 (permalink)  
Old 18-July-2007, 08:43 PM
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