Hydrostatic Pressure

[Freddy86]

Hydrostatic pressure is exerted in all directions but what determines whether it acts radially inwards or radially outwards. For example, if you are a diver you feel pressure from the water acting inwards, giving you a crushing sensation. However, if you fill a balloon full of water and poke holes in it, the pressure acts radially outwards?

 

[russ_watters]

Divers do not get a crushing sensation. That would be awful and no one would want to do it!

The pressure pushes a balloon out because there is a higher pressure inside than outside.

 

[dauto]

If the pressure is larger inside, the net force will be outwards. If the pressure is larger outside, the net force will be inwards. In the case of a diver the forces are equal (just about) with no net force.

 

[Freddy86]

Divers do not get a crushing sensation. That would be awful and no one would want to do it!

The pressure pushes a balloon out because there is a higher pressure inside than outside.

Thanks for the replies. So if you submerge an object in a jug of water then the pressure will be radially inwards on this object right? Is this because the walls of the jug are considered to be at greater pressure than the fluid then?

No I meant that if a diver went down too deep they get a sense of being squeezed (maybe crush is too drastic). I thought this was why the depth of snorkeling is limited as the deeper you go the more your chest gets squeezed so at a particular depth you cannot expand your diaphragm anymore and are thus are unable to breath.

 

[dauto]

You cannot snorkel very deep because you breath out of the air above which is indeed at a lower pressure, but you can scuba because then you breath out of a pressurized container. You didn't specify which one you're talking about.

 

[russ_watters]

Thanks for the replies. So if you submerge an object in a jug of water then the pressure will be radially inwards on this object right? Is this because the walls of the jug are considered to be at greater pressure than the fluid then?

The walls will constrain the liquid, yes - otherwise it would break and all the water would pour out.

No I meant that if a diver went down too deep they get a sense of being squeezed (maybe crush is too drastic). I thought this was why the depth of snorkeling is limited as the deeper you go the more your chest gets squeezed so at a particular depth you cannot expand your diaphragm anymore and are thus are unable to breath.

"Diving" typically means scuba diving. It isn't the same as snorkeling. dauto is right; for snorkeling, you have to fight the water pressure to breathe (as does your snorkel - if it isn't rigid it will collapse). But for scuba diving, you don't.