Outward Expansion starts fast, then slows down. Inward Expansion speeds up. A typical Outward Expansion, say from an explosion, begins quickly, but stops. Inward Expansion, say from the nozzle of an operating Central-Vac, placed in the middle of a room, speeds up gradually, all the way to terminal speed.

Many people are unfamiliar with Inward Expansion, but if this Central-Vac evacuates the air from the center of the room, surrounding air will move in, expanding, and picking up speed, to fill the void. Am I right or wrong?

This is scarily reminiscent of an idea called "conspansion" from the "CTMU"...

I won't get further into it here, though. If interested, ask Mr. Google to help you out.

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"...wait for the ricochet."

"Inward expansion" sounds like an oxymoron.

It's generally called an "implosion".

Hehe, yeah. What he said.

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"...wait for the ricochet."

CTMU - I went there. Wow, talk about complex. No, I'm just looking for some agreement on this terribly basic observation of mine. I mean, everybody knows about this outward expansion for example, if you inflate a baloon - but doesn't it just reach a point where it's hardly expanding any more. I mean, past that point, you're just increasing the pressure, with very little expansion happening. That continues, this lack of expansion, probably right untill the balloon explodes. Can I get some agreement?

I haven't blown up a balloon lately, but I believe you're right - it's easy to blow up the balloon initially, but at a certain point you start stretching the material of the balloon too much (at which point its tensile strength kicks in). Further expansion beyond that point causes it to fail catastrophically (i.e. explode).

Best way to see for sure is to try blowing up a balloon and see what happens

Good point. Me, I call it a paradox. I say, it's paradoxical, how something can expand inwardly, but the air moving towards that Vacuum-Cleaner wasn't it Losing Pressure? And according to Boyle's Law, isn't that the same Increasing Volume? I mean, is that the Law, or isn't it?

And doesn't 'common sense' tell us that Increasing Volume is simply another way to say Expansion? Definitely, I would call it a paradox, how Inward Expansion can even happen, but my observations have shown me - Time and Time again, that it is, in fact, the reality.

Yes, but, according to Wiki, it's not the kind exampled by the sub being crushed from the outside - an implosion, of course, but one of 'fluid dynamics', by one Victor Schauberger, who said a suction from inside causes an implosion, a movement pedicentral, but not straight radially to the center, but as a vortex.

I'm just quoting Wiki, on the subject of 'implosion,' so help me. I wish everybody would go there. Read it for yourself - fluid dynamics... Victor Schauberger - it's highly interesting. Tho' it does say, his work was not generally accepted...

So yes, it's called an implosion. Only what's the opposite to 'implosion'?

It's 'exploding', isn't it? I know it's semantics, but I still like my 'inward expansion', which I hold to be the opposite of 'outward expansion'.

The two things are different, but real, to me. But 'implosion' is fine too - as long as it's from the inside a la Victor Schauberger

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).

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"...wait for the ricochet."

Vacuum cleaners don't really make a vacuum, they just shift air along with a fan [though I suppose if the fan was fast enough you might get a cavitation effect (like when a boat propeller goes "too fast" in water)].

Although your central vacuum cleaner system will appear to make air speed up, that's a fairly understandable.

The cleaner is removing a given volume of air from the room (and sending it to where-ever the filter system is). The air at the nozzle will be moving at whatever speed.

The air that comes into the room to replace the shifted air, will come from all over the place. That spreads the given volume of air out over many locations - the speed of air at all those air sources can then be lower.

If you completely sealed your room, and just left a vacuum cleaner nozzle sized hole in the wall for air to get in, the air comming in that hole would be moving at the same speed as the air dissappearing down the tube.

(Ignoring the "elasticity" (due to compressibility) of the air which will have some effect.)

Of course, as the air comming through that hole enters the room, it would "spread out" into the room and go "slower", while air getting to the nozzle would appear to "speed up".

I don't think that's any different than looking at a river. At the narrows, the water "speeds up", and when the river widens again, the water "slows down".

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Measure once. Cut twice. Power tools are fun.

Well,it was just an analogy.

Yeah, well thanks for agreeing with me, anyway.

Yes, well I think, as I say, that everybody knows about this 'outward' expansion.
I'm more concerned with the inward kind. It seems to me, right now, that this is a 'desert' of scientific thinking. I mean, everywhere there's a Lowering Pressure there's Increasing Expansion - assuming Temperature and other things aren't factors.

This Increasing Expansion is important, I feel.

.Of course you're right, they don't necessarily pull 30 inches of mercury, but they do lower the pressure, and they do expand the air they take into the nozzle.

'Cavitation' is right under 'implosion' in Wiki.

Now hold on here! That air is moving at maximum speed. That air is travelling at its Terminal Velocity.

Here, air-speeds will be minimal. This air is barely moving.

That air will be Slowing Down as it leaves the hole. Whether it's one hole or many - once inside the room (the boundary for this experiment) the air will assume its minimum speed.

(Ignoring the "elasticity" (due to compressibility) of the air which will have some effect.)

Glad you can see, that once the air is in the room, and part of the experiment, it will Speed up on the way to the nozzle.

I guess so, but that's a different experiment, no? But it's interesting, isn't it, that at the 'narrows', the river Speeds Up.

You'd almost expect it to Slow Down at the restriction. To me, it's another (or maybe the same) paradox - that according to Bernoulli, this 'restricted' river should, here, Speed Up. I'm right, aren't I?

Notice also, however, that as the water 'narrows' it gets deeper, and a given volume of water needs to get through that 'pinch' in a certain amount of time, hence, it 'speeds up' (provided there's more water coming downstream from above the pinch to provide the 'motivation').

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"...wait for the ricochet."

Why is this in ATM? All I see are rather elementary questions and answers about familiar fluid-dynamics phenomena. What unorthodox theory, if any, is being proposed?

Umm...

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"...wait for the ricochet."

No.

That air is moving as fast as the fan in the vacuum cleaner can make it move.

My vacuum cleaner (regular portable thing) has a speed setting slider.

That affects the speed of the fan motor; that affects the speed of the air movement; and that affects the amount of cat-hair-sucking ability.

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Measure once. Cut twice. Power tools are fun.

Just wait a wee bit and then the vortices will come calling, and the old thread can be picked up again about clumping up etc. etc. There are still a load of unanswered questions in that thread, which is closed at this point untill astrocat reopens it again.

For the rest, astrocat should first read a book on physics, especially the part on gas dynamics etc. It can all be calculated by the simple continuity equation: div(rho v) = 0, the divergence of the product of density and velocity (a vector) for a closed system is zero (i.e. there are no sources of new stuff in the system), where the divergence operator is given by div(A) = dA_x/dx + dA_y/dy + dA_z/dz, and do not forget the chain rule for in the above case A = rho v.

And there is nothing "paradoxical" about inward expansion, but it definitely is an "oxymoron".

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Optimism does not change the laws of physics. (T'Pol)
A good scientist has freed himself of concepts and keeps his mind open to what is. (Dao De Jing 27)
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Martin ( http://www.geocities.com/DrMartinV )

Now I can see the possibility that astrocat is attempting to buy time by spending a few days going through the motions of building a consensus on a topic about which there is no real controversy, and then co-opting it for pushing a real ATM idea in another thread. I would recommend that we abstain from further participation in this one.