PRESSURE IN LIQUIDS

Have you read or been told that liquid water can’t be compressed? In a simplistic sense, this is true, but it doesn’t mean liquid water never exerts pressure. Liquids can and do exert pressure, as anyone who has been in a flood or a hurricane or a submarine will tell you. You can experience “water pressure” for yourself by diving down several feet in a swimming pool and noting the sensation the water produces as it presses against your eardrums.
In a fluid, the pressure, which is defined in terms of force per unit area, is directly proportional to the depth. Pressure is also directly proportional to the weight density of the liquid. Let d_w be the weight density of a liquid (in newtons per meter cubed), and let s be the depth below the surface (in meters). Then the pressure P (in newtons per meter squared) is given by
P = d_ws
If we are given the mass density d_m (in kilograms per meter cubed) rather than the weight density, the formula becomes
P = 9.81d_ms