## Why does pressure in a liquid not depend on the volume?

Question

Don’t include equations/ proofs in your answer, I want to know why does it physically/qualitatively make sense that the pressure in a liquid does not depend on the volume.

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General Physics
5 years
1 Answer
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## Answer ( 1 )

Pressure is measured as force per unit area.

Working on an open tank of some height for simplicity:

The pressure in a liquid is in effect purely down to that in a column with a cross-section the size of the measuring unit – eg. one square centimetre or one square inch etc.

The force in ever other hypothetical “column” of that size in the tank is being applied to something other than the one you are measuring, so is irrelevant.

The tank could be an inch across or a mile across, the mass – weight – force on the column you are measuring is the same regardless.

As an example, imagine a tankful of piles of discs, all stacks the same height (eg. stacks of identical coins or washers).

If does not matter how many stacks there are, one or a million – the weight of one stack (and so force per unit area) is proportional to the height of the stack, not how many others there are.