Pressure, P is the force applied per unit area of a surface. It is calculated like this:
P= F/A
Where
F= force in Newtons
A= area in m²
Pressure is measured in Pascals (or N/m²).
For example, standing on one foot places more pressure on that foot than when you are standing on two feet because the force from the weight of your body is distributed over less area.
As you can see, though the force is the same, as the area is increased, the pressure decreases.
Example: What is the pressure exerted on the base of a computer monitor of area 30 cm² when the monitor has a weight of 400N?
P= F/A
= 400N/0.3 m²
= 1333.33 Pa
Fluid pressure is a measurement of the force per unit area on a object within a fluid or on the surface of a closed container. Because a fluid has no definite shape, it exerts pressure in all directions.
At a certain point in a fluid, the pressure depends of the depth of the point, the density of the fluid and the force of gravity. At that certain point at a certain depth in a fluid, there is an amount of fluid above that point exerting pressure on it.
All points at the same depth in a fluid have the same pressure.
Fluid pressure is calculated like this:
∆P=ρg∆h
Archimedes' Principle
This principle is all about buoyancy/floating. Archimedes' Principle states that the buoyant force exerted by a fluid on an object is equal to the weight of fluid displaced.
If the weight of fluid displaced is more than or equal to the weight of the object, the object will float.
If the weight of fluid displaced is less than the weight of the object, object will sink.