We can understand how pressure in water depends on depth by considering a stack of bricks.?

Question

The pressure below the bottom brick is determined by the weight of the entire stack. Halfway up the stack, the pressure is half because the weight of the bricks above is half. To explain atmospheric pressure, we should consider compressible bricks, like those made of foam rubber. Why is this so? Thanks for your help!!

Answer 1

that's actually a fairly reasonable analogy.

since water is, for all intents, not compressible, you don't need to worry about that.

for a more accurate comparison, use hardwood blocks, because their density fairly closely resembles that of water.

one time, many years ago, i thought to myself, "self, why do divers go to all that trouble?  why don't they just get a hose, hang on to it with their teeth, and when they want to breathe, just suck.  Hmmmm, how do i test?  OH, i know, get a bucket of water and see how far i can suck water up the hose.  so i did,  2-3-4 feet was all i could manage."  i guess that's why divers use all that equipment.

finally, air pressure is pretty high.

if you swim under water, when you're down 33 feet, you've doubled the pressure on your body, compared to being on the surface.

if you've a well, you can draw water up 15-20 feet.

if the water is 40 feet down, that's impossible.

you can only pull the water 33 feet up.

after that, you just create a vacuum, and the water won't come up any more.

you have to put the pump down the hole and push the water up.

Answer 2

Air is compressible but since the pressure is uniform, the brick analogy works just fine for atmosphere also.

Answer 3

liquid water is not very compressible, whereas gaseous air is very compressible.