Equal Pressure Canister Collapse

• Airman
In summary, the conversation discusses the possibility of a flimsy canister collapsing or imploding under equal pressure on the inside and outside due to a greater outside surface area than inside. It is concluded that this is possible, using examples such as marshmallows and aerogel, and is supported by Pascal's hydraulic paradox. The idea that force is a vector and the balance of forces is explained, and resources are provided for further understanding of the concept.
Airman
Say you had a very flimsy canister. Would it be possible for it to collapse or implode even if the pressure inside it and the pressure outside of it were equal, due to the fact that it has thickness and therefor a greater outside surface area than inside surface area? If so, are there real life examples of is this "effect", or is it negligible all the time?

No, not possible.

Okay why? What am I thinking wrong here:

I'll assume a cylinder has an inner radius of 1 and a thickness of 1. The inner surface area would be h(pi)(1)^2 or h*pi, and the outer surface area would be h(pi)(2)^2 or 4*pi. (I'm neglecting the ends, which are equal). So whatever the pressure is, it exerts 4 times the force on the cylinder from outside than inside. Wouldn't this put stress on the cylinder and crush it if the material was weak enough?

A surface has no thickness and has the same area on the inside and out. You are talking about two different surfaces.

The material can't be that weak or else it will not be a material at that pressure.

You can say the same thing about a piece of paper, it is getting crushed from both sides by the atmosphere.

This is an interesting question, one way to think about it is to draw a cutout (a "wedge") of the cylinder and pretend like it is glued on lightly on the cylinder. Then think about what type of forces the glue will experience.

This is actually a form of the old Pascals hydraulic paradox.

I know I must be talking about two different surfaces as I have two different surface areas.

Yes but the paper is experiencing the nearly the same force on both sides. For my object the force is much greater on one of the surfaces. If the internal structure isn't strong enough in my object wouldn't the inside and outside surfaces be pushed together? Is that what you mean by it not being a material? As it wouldn't retain it's integrity?

Doesn't Pascal's Hydraulics Paradox support this idea?

I'm sorry this is just bothering me and I still can't grasp the idea in my mind.

Airman said:
Say you had a very flimsy canister. Would it be possible for it to collapse or implode even if the pressure inside it and the pressure outside of it were equal, due to the fact that it has thickness and therefor a greater outside surface area than inside surface area? If so, are there real life examples of is this "effect", or is it negligible all the time?
In a way yes. For example, a marshmellow (or a piece of aerogel), which you can just think of as a cannister with zero internal surface area, is partially collapsed or crushed by the surrounding air pressure.

(Note especially the conclusion: if it is exposed to the air pressure suddenly, it might even implode or tear.)

Airman said:
Okay why? What am I thinking wrong here:

I'll assume a cylinder has an inner radius of 1 and a thickness of 1. The inner surface area would be h(pi)(1)^2 or h*pi, and the outer surface area would be h(pi)(2)^2 or 4*pi. (I'm neglecting the ends, which are equal). So whatever the pressure is, it exerts 4 times the force on the cylinder from outside than inside. Wouldn't this put stress on the cylinder and crush it if the material was weak enough?
Remember that force is a vector. If your cannister is closed, the total force on the outside is zero (because the normal force on the outer left balances the normal force on the outer right). Likewise, the total force integrated over all the inner surface is also zero.

If the cannister is open, then these two total forces may not be zero, but they will be opposite and always exactly equal in strength.

As an example (much as Curl is suggesting) draw a square, and inside that draw a diamond, and let this diagram be the cross section of your (prism shaped) cannister. Now consider just one quarter of the sidewall: the cross section is a right angle triangle where two outer sides have equal length and the inner hypotenuse is shorter than the total of the outer sides. So the inside has less area than the outside, but the force from the outside is still in balance with the force from the inside, because the force from the outside has two components that partially cancel each other out.

In actual fact (as is obvious if you imagine our container is sculpted from aerogel) these external forces will compress surfaces of the container, until the internal pressure in the material increases to about the same as the external pressure. At that point, the inward force on some particular atom located on the outer surface will be equal to the outward force directed on that same atom, and so on for every other atom that is located anywhere else in the material of the container, so the shape will have reached a stable equilibrium.

Airman said:
Doesn't Pascal's Hydraulics Paradox support this idea?

I'm sorry this is just bothering me and I still can't grasp the idea in my mind.
Do you see how the apparatus will behave in real life, and why?

Last edited by a moderator:

http://scubageek.com/articles/wwwhyd.html

Thanks again my mind is now at peace with the question.

1. What is Equal Pressure Canister Collapse?

Equal Pressure Canister Collapse is a phenomenon in which a sealed canister containing gas or liquid collapses due to a decrease in external pressure.

2. What causes Equal Pressure Canister Collapse?

The decrease in external pressure causes the pressure inside the canister to become greater than the pressure outside, resulting in the canister collapsing in order to equalize the pressure.

3. What are some examples of Equal Pressure Canister Collapse?

Equal Pressure Canister Collapse can occur in various situations, such as when a can of soda is opened at high altitudes, when a vacuum-sealed container is transported to a lower elevation, or when a diving tank is brought up to the surface.

4. How can Equal Pressure Canister Collapse be prevented?

To prevent Equal Pressure Canister Collapse, the pressure inside the canister should be equalized with the pressure outside before opening or transporting the canister. This can be done by slowly releasing small amounts of gas or liquid from the canister.

5. Are there any safety concerns with Equal Pressure Canister Collapse?

Yes, Equal Pressure Canister Collapse can potentially cause injury if the collapsing canister is not handled properly. It is important to follow proper safety precautions when dealing with sealed canisters to prevent accidents or injuries.

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