I thought water was non-compressible

For the same reason atmospheric pressure changes with altitude. The pressure is dependent on the vertical height of the column of fluid (air or water) above the point of measurement.

Compressing a fluid heats it. But if one compresses water to some pretty extreme pressures it will behave as though it is crystalline at high temperatures ~ 70,000 atmospheres.
 
I don't understand the question, but I think asking why air pressure increases with depth might help you.

And I think the answer is in the link you provided:
The deeper the object is placed in the fluid, the more pressure it experiences. This is because is the weight of the fluid above it.

What makes you think water pressure is static?
 
Because of the weight of the column of water above it.

Dive to the bottom of a swimming pool and see if your ears feel the difference.
 
"Non-compressible" means the VOLUME (or equivalently, the DENSITY) of the water doesn't change appreciably unless the pressure is VERY high. It doesn't mean that its surroundings can't exert pressure on it, and vice versa. In fact, it HAS TO be acted on by pressure force if you think about it. Imagine a quantity of water sitting still somewhere in the middle of a lake, well under the surface. If it's not to be accelerated downward, there has to be a force on it to balance gravity. Where does that force come from? The pressure exerted by the water next to it (especially below it)!

That's a pretty simplistic argument and doesn't get into what happens at the microscopic level, but it's essentially correct and can be extended to show why pressure increases with depth (hint: the weight of all the water above our imaginary volume of water is another downward force, in addition to gravity, that must be balanced).
 
dmspilot said:
The deeper the object is placed in the fluid, the more pressure it experiences. This is because is the weight of the fluid above it.
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Add to this - the weight of the fluid, INCLUDING THE AIR above it.

Air compresses, so we have the phenomenon of thinner air at higher altitudes. You do NOT get thicker water with depth, the water is not compressing. The water is the same volume, but because it is being pushed down by all the stuff above it, the water is under pressure. Put something down there with anything compressible in it and the water will try to force that same thing to compress until it's at the same pressure as the water.

25 years ago I was on a submarine in the Navy and dealt with this all the time. One neat trick was to take a soft 8 oz styrofoam cup and trap it in a free flood area outside the hull. While we were underwater and deep, the air was squeezed out of the cup. After surfacing, the 8 oz cup would come back as a little 1 oz shot glass and no longer soft. All the air had been compressed out of it by the surrounding water.

Some easy numbers. These are not exact, but are good estimates. Pressure at sea level is approximately 15psi (Pounds per Square Inch). When go under water, that pressure goes up by 15 psi every 33 feet that you go down OR 45 psi for every 100 feet. If you scuba dive to 100', you are breathing air that is at 60 psi because that is the weight of the water and air above you. If you held your breath and swam for the surface, the pressure on the air in your lungs would go down, the air would expand and your lungs would burst because you have about 4 times as much air as you can hold at the surface.

You can see the same thing with a beach ball - take the ball and swim down 20' into a deep pool. The ball will become flat because the weight of the water is pushing in on the ball, compressing the air until the volume decreases to the point that the air pressure equals the weight of all the water and air above it. At 20', roughly 20 psi.

Air compresses. Water does not.
 
Was taught that water was "for all practical purposes" non-compressible. Since water can have varying amounts of air in it, it can show slight signs of compressibility.
 
Got to love it. Citizen science. LOL
For fresh water at 60 degrees, 0.433 psi/ft is a good approximation of the change in pressure with depth. That number is simply the weight of a cubic foot of water, 62.4 pounds/cubic foot, divided by the area of a square foot in inches (144).

For some engineering purposes, the compressibility of liquid water is about 3 x 10 ^-6 v/v/psi. Yes, in some circumstances the compressibility is important.
 
Van Johnston said:
Because of the weight of the column of water above it.

Dive to the bottom of a swimming pool and see if your ears feel the difference.
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But that is not due to water compressibility, it's due to the compressibility of the AIR behind your eardrum. Water pressure increases with depth due, as you mentioned, to the weight of the water above. But water itself does not compress. A diver can go to any depth and not be crushed because his tissues are essentially water and not compressed by the surrounding water. Only the *air* spaces in his body have to be pressure-equalized to the surrounding water pressure to avoid damage.

Submarines only have to have strong hulls because they are filled with air at surface atmospheric pressure. If the air inside were kept at the same pressure as the surrounding water, there would be no limit to the dive depth of a submarine. But it leads to a whole host of other problems like decompression when the crew wants to return to the surface.
 
Wonder if we can get those bricks to follow Boyle's law.
 
A one inch square column of water 1 ft.tall placed on a scale would weigh 0.433 lbs. Make it 2 ft. tall and it would weigh 0.866 lbs. Put a pressure gage in place of the scale and you would get the same numbers as pounds per square inch. Since the gage is is seeing pressure (force per unit area) it doesn't care what the cross section of the column of water is , just its height. The only thing that compressibility has to do with it is that the weight of the column with height varies linearly with a non compressible fluid and non linearly with a compressible fluid.
 
Pascal, that tricky bastard from Clermont-Ferrand, France, documented a law dealing with this very question:

https://en.wikipedia.org/wiki/Pascal's_law

States that:
...pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid such that the pressure variations (initial differences) remain the same.
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Ever 33 ft. of sea water(salt) equals 14.5 psi or 1 atmosphere as we called it. the weight of the air above you equals 14.5 psi, or atmospheric pressure. Water does not compress but the weight of the water stacked up is what equals pressure that effects you when diving. In sea water testing for saturation diving they have pressed divers down to 2100ft. of sea water, it took six weeks to decompress after that but other than that the possibility of putting humans down as deep as you want is almost endless. The record for deepest dive in the Gulf of Mexico is 1056ft.
 
Checkout_my_Six said:
yup....bout the same result as a ton of feathers too. :D
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No,mthe feathers won't stack tightly like the bricks,and will spread out a lot, putting weight on the ground instead of only on you. But it would be a lot of feathers! They also aren't hard as a brick . . .
 
Jaybird180 said:
...then why does water exert more pressure on all exposed surfaces of an object submerged in it as depth is increased?

https://www.grc.nasa.gov/www/k-12/WindTunnel/Activities/fluid_pressure.html

Why would the pressure vary with depth since its static?

Additionally, how do you calculate the theoretical high-pressure point at which liquid water could become ice?
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I think your confusion lies in this question, why would incompressiblity make the pressure static?
 
So I have a leak in my integrated fuel tank. I'm going to find the leak by adding about 2 psi to the tank after I coat the seams with soapy water. How you ask do I pressurize the tank. I have a clear vinyl tube that I will attach to the vent. I will "T" off a short tube to a valve. The tube will then run down to the floor in a "U" and up a 4 foot board with measured markings. I will fill the tube with enough water to get it to the one foot mark on the board. By blowing in the valve, I will pressurize the tank and the water will rise about three feet to hold the pressure on the tank. I can only do this BECAUSE THE WATER IS INCOMPRESSIBLE.
 
Hank S said:
No,mthe feathers won't stack tightly like the bricks,and will spread out a lot, putting weight on the ground instead of only on you. But it would be a lot of feathers! They also aren't hard as a brick . . .
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no....try it with horse feathers. They'll stack better. ;)
 
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No matter how deep you go into the swimming pool on the international space station, you're still at surface pressure.
 
azure said:
Yes, I didn't read it carefully but the first two sentences are correct. It takes a huge amount of pressure to compress water to any appreciable degree.
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Devine "huge". Perhaps the compressibility becomes important with large volumes of water at moderate pressures?
 
Clark1961 said:
Devine "huge". Perhaps the compressibility becomes important with large volumes of water at moderate pressures?
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Nope. At livable temperatures, water is compressible by 0.000053%. Even at 150 atmospheres (2200psi), water compresses less than 1%.

For the mathematically addicted, visit here for a decent, clear explanation: http://hyperphysics.phy-astr.gsu.edu/hbase/permot3.html. Compressibility does not become important with large volumes of water at most pressures. That is how the fire dept can pump water out of hoses at very high pressures to reach the upper floors of buildings--they apply pressure to the water and instead of compressing, it moves. Water can be squirted much farther than air, which is very compressible.
 
Hank S said:
Nope. At livable temperatures, water is compressible by 0.000053%. Even at 150 atmospheres (2200psi), water compresses less than 1%.

For the mathematically addicted, visit here for a decent, clear explanation: http://hyperphysics.phy-astr.gsu.edu/hbase/permot3.html. Compressibility does not become important with large volumes of water at most pressures. That is how the fire dept can pump water out of hoses at very high pressures to reach the upper floors of buildings--they apply pressure to the water and instead of compressing, it moves. Water can be squirted much farther than air, which is very compressible.
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They are not saying that it doesn't compress at all, only that the compression is very small.

A common statement is that water is an incompressible fluid. This is not strictly true, as indicated by its finite bulk modulus, but the amount of compression is very small.
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I don't think your fire hose analogy means too much because even if water compressed 10, 20, or more percent, it would still come out of a hose under pressure, just not as much.
 
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