The four properties
The four activities so far have given us four facts about liquid pressure. Let us set them down together as the properties of liquid pressure.
(i) It depends on the height
The pressure at a place inside a liquid depends on the height of the liquid column above it. As that height increases the pressure increases, and as it falls the pressure falls.
(ii) It is equal at equal levels
At all points lying at the same level in the liquid, the pressures are equal.
(iii) The same value in every direction
At a place inside the liquid, the pressure takes the same value in any direction.
(iv) It does not depend on the shape
Liquid pressure does not depend on the shape of the liquid column; it depends only on the vertical height of that column.
Read (i) and (iv) together
Taken together these two make a very strong statement: the only measurement that fixes the pressure at a point inside a liquid is the vertical height of the liquid column above it. The shape of the vessel, its width and the total amount of liquid in it make no difference at all.
On the next page we turn that statement into a formula — knowing the height of the column and the density of the liquid will be enough to calculate the pressure.