Homework Help: Pressure on an item underwater

2112 · Jan 11, 2007

When an item is submerged underwater, I believe that pressure from the surrounding water is equal in pressure around the item except from beneath, is this correct?

Hootenanny · Jan 11, 2007

2112 said: ↑

When an item is submerged underwater, I believe that pressure from the surrounding water is equal in pressure around the item except from beneath, is this correct?

The pressure exerted by a liquid increases linearly with depth, i.e. the deeper you go the more pressure is exerted. However, this pressure is exerted uniformly at a certain 'level' in all directions. Therefore, there is a greater force (note force not pressure) pushing a submerged object upwards than downwards; i.e. there is a net force upwards. This is buoyancy.

2112 · Jan 11, 2007

If you might indulge me,? , if I wanted to pump air too, say a depth of eight feet, and I only was equipped with something with a low psi, (very minimal psi), how would it be easier to have the air break the barrier of pressure/force to escape its chamber?
Would I have a better chance at trying to get the low pressure air out by pointing it upwards or down, (at that eight foot level).
Before I forget there is a sort of check valve on it that won't let water through its outlet, but air can move freely throught it.

Hootenanny · Jan 12, 2007

With a little thought and be reading what I have posted above, you should be able to answer this question yourself.

DaveC426913 · Jan 12, 2007

2112 said: ↑

If you might indulge me,? , if I wanted to pump air too, say a depth of eight feet, and I only was equipped with something with a low psi, (very minimal psi), how would it be easier to have the air break the barrier of pressure/force to escape its chamber?
Would I have a better chance at trying to get the low pressure air out by pointing it upwards or down, (at that eight foot level).
Before I forget there is a sort of check valve on it that won't let water through its outlet, but air can move freely throught it.

I'm confused. Are you pumping air down? "pump air too, say a depth of eight feet"
Or are you pumping the air up? "escape its chamber?", "get the low pressure air out by pointing it upwards or down, (at that eight foot level)."

2112 · Jan 12, 2007

The air goes down through a hose to a depth of 8 foot, I just wondered how best under the circumstances could I get an air bubble come up from that depth.

DaveC426913 · Jan 13, 2007

Well, unless your container at the 8 foot level is both rigid in structure and held securely in place, the air down there will happily come up from that depth without any help from you... Your container will implode, or it will rocket to the surface.

OTOH, if it is both those things, then you move air to and fro with free abandon. You could blow in it if you chose.

Look, it seems tome you're beating around the bush. I think you're going to need to illustrate what you are talking about if you want meaningful answers.

2112 · Jan 13, 2007

Thanks for the answers, you gave me a better understanding of force and pressure and I appreciate the help!