Pressure (I)

Mathematical expression

2 / 2

The calculation which is shown on the previous page in a sequential manner is presented below in a more traditional way.

We can imagine in a mass of water a portion of water with a cylindrical form. The weight of the column of liquid which is above it (in light blue in the illustration) acts on the surface of the lower side S, at a depth h. We will call the mass of this column m, its volume V and its density d. We know that
m = d •V and that V = S• h so we have:
The weight of the column of water = m•g = d•V•g = d•g•S•h
This weight acts on the surface S, exerting a pressure p, called hydrostatic pressure:
p = the weight of the column of water /surface area = d•g•S•h / S = d•g•h

In the previous visual you could see how the pressure varied with the density of the liquid and how at a point situated in a jutting edge the pressure was the same as at other points at the same depth.

	Mathematical expression
	The pressure increases the deeper you go in liquids
	Which goes the furthest?
	A little goes a long way!
	Communicating vessels
	Syphons