Zero Psi with a potential of 2000psi????

Quantum Quack

Quantum Quack

Life's a tease...
Valued Senior Member
Hi guys, just a simple question of how conventional thought deals with this scenario.

<img src=http://www.ozziesnaps.com/vacram.gif>

We have three rams. All are assembled in a space vacuum. For all intents and purposes all three rams have zero psi. figure A

Now if we pump 2000psi into the outer two rams do we still have zero psi in the middle ram? [ the outer rams act against the inner ram attempting to decrease the pressure in that ram.]

I am under the impression that the answer is that the inner ram still maintains a zero psi state yet that zero psi state is inhibiting the outer rams that are at 2000psi.

Is the pressure in the inner ram [ fig B] "really" still only zero psi or something else?
I was told a while ago that pressure can never be less than zero, is this valid?

Has the vacuum in the inner ram achieved a state of a 2000psi potential? yet is maintaining a zero psi state?
How does physics handle the forces in this situation?

Thanks in advance..... :)
 
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If A and B are in a vacuum, the middle piston is in equilibrium with environment and can be ignored. Or are the rams not in a vacuum?
 
a_ht said:
If A and B are in a vacuum, the middle piston is in equilibrium with environment and can be ignored. Or are the rams not in a vacuum?
Click to expand...
all rams are sealed from the vacuum ambience.

The outer rams exert an outward force on the inner ram that was zero psi or vacuum to start with. [ it is a sealed pressure vessel just like the outer rams]

They were assembled in the vacuum of space only for convenience.
 
My bank account is the only thing I know of that has the proven ability to be less than nothing. QQ, is this a joke?
 
essentially i guess i am also asking whether a pure vacuum can be de-compressed further. And if not how are the counter forces accounted for.
 
CANGAS said:
My bank account is the only thing I know of that has the proven ability to be less than nothing. QQ, is this a joke?
Click to expand...

ha...me too , me too.....ha mine actually has teh proven disability of never being more than nothing.... :D

Seriously though as pressure can never be less than zero how is it that it gains a potential of [in this case] 2000psi.....whilst maintaining a zero psi state?
 
Picture a mercury barometre in the atmosphere, the liquid raises to 760mm (i think) before creating a vacuum on the upper part of the hermitic cylinder. The lenght of the upper part could in principle be increased indefinetly and it would not change the height of the liquid. Showing that vacuum cannot be less than zero.
 
The thing is ....we have a force being exerted on that vacuum of 2000psi.
The vacuum allows this pressure of 2000psi to exist. Yet it remains as zero psi.

So what is actually happening to our vacuum according to physics?
It is zero psi but surely it has other attributes given that it is withstanding a force of 2000psi???
 
vacuum6jd.jpg


x will increase until Fp - Fair - Fv = 0. If you increase the amount of psi in the pressurized piston, x will increase proportionnaly. And notice that the pressure of 2000psi will decrease as x gets bigger... until it equals the vaccum + air pressure.
 
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in the problem i mentionned above. Fv is a constant. Fair is also a constant. Fp inversionnaly proportional to x. so the answer to your question is that ram B is not at equilibrium.
 
QQ: In your diagram you showed no mechanical restraints. As soon as the rams began to be pressurised the assembly would blow apart. If mechanical restraints are implied, then a subtle answer to your subtle question is that the original configuration has the zero psi chamber acting as a Casimir Effect cavity with an extremely little NON-HYDRAULIC pressure from the trapped virtual photons and other virtual particles. In the implied expanded but restrained configuration a larger cavity would, according to Casimir Effect, trap virtual stuff of greater wavelengths in addition to shorter wavelengths previously trapped. More energy and therefore more NON-HYDRAULIC Casimir pressure would exist. So, we would start with no psi and extremely little Casimir pressure in the chamber and wind up with no psi and slightly more than extremely little Casimir pressure. :cool:
 
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Quantum Quack said:
I am under the impression that the answer is that the inner ram still maintains a zero psi state yet that zero psi state is inhibiting the outer rams that are at 2000psi.
Click to expand...

The inner ram is not inhibiting anything. There is nothing stopping the outer rams from expanding.
 
Pete said:
The inner ram is not inhibiting anything. There is nothing stopping the outer rams from expanding.
Click to expand...

Assume a sturdy assembly. And that as the outer rams attempt to expand the inner chamber rams, the inner chamber rams would have to separate ...yes?
However if the inner rams act against zero pressure, for it to expand the pressure would have to drop which it can't. [ the inner ram is a sealed assembly ]

I have redrawn the diagram and hope it is easier to understand:
<img src=http://www.ozziesnaps.com/vacram2.gif>

The inner ram is a vacuum chamber that has two opposite outward forced rams acting against that vacuum.....
The blue lines are pistons attempting to increase their separation

Hopefully that makes more sense....
 
With no mechanical restraints and no external pressure your assembly would fly apart quite rapidly. As it flies apart each half of the assembly would acquire a kinetic energy up to V*2000psi where V is the volume of one ram. (e.g. if each ram were 1 gallon then the max KE would be about 50 btu, since we are using English units)

You are correct, you cannot have a negative absolute pressure because you cannot have a negative amount of matter inside a container. You can, however, have a negative gauge pressure. In other words, if your rams were at sea level, rather than in space, a perfect vacuum in the middle ram would cause a -1atm pressure difference between the outside and the inside.

-Dale
 
Again, the force generated by the vacuum piston is constant, it does not increase with lenght.
 
Hi QQ,
Quantum Quack said:
However if the inner rams act against zero pressure, for it to expand the pressure would have to drop which it can't.
Click to expand...

Think carefully. I know that there is a particular relationship between pressure and volume that you have in mind (perhaps indirectly), but I'm not sure that you've thought about it in a mathematical form.

How does pressure relate to volume mathematically (if everything else is constant)?
 
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Equal to zero if the ram is in a vacuum, equal to a negative value if the ram is in a pressurized environment. Pretty much what you are saying in an earlier post.
 
Precisely, a_ht.

PV=nRT. For n=0 P=0 regardless of V. The inside of the piston is always at zero absolute pressure. The gauge pressure will always equal the negative of the environmental pressure.

For the ram-in-space case environmental pressure = 0 so no force. For the sea level case environmental pressure = 1 atm, gauge pressure = -1 atm, and the force will be -1 atm times the area of the piston.

-Dale
 
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