## Pressure in a Liquid

Liquids exert a pressure on anything in them. The pressure is due the amount of liquid or gas pushing down on it. In fact the atmosphere pushes down with a force of about
$10^5N$
(the weight of about 10 medium sized cars) on every square metre.
The pressure exerted by water is especially significant because there is so much of it on Earth. Water is virtually incompressible, so the density is nearly constant. If
$\rho , \: g, \: h$
are the density of water, acceleration due to gravity and the depth of water at a point respectively, then the water pressure at that point is
$P_{Water}= \rho g h$
.
To find the total pressure we must add to this the atmospheric pressure
$P_{Atmospheric}$
then
$P_{Total}=P_{Atmospheric} + \rho gh$
.
Water is about 800 times denser than air at sea level, and water pressure increases rapidly with depth - the equivalent of 1 atmosphere of pressure for every 10m of water depth.