The rest of this chapter will deal with forces that originate from pressure, more specifically fluid pressure. Technically, pressure is associated with solids as well as liquids and gases. But the concept is especially useful in relation to fluids, so it tends to be associated more with liquids and gases.
The meaning of pressure
So what is pressure? It is the normal (perpendicular) force per unit area exerted on the surface of an object. The origin of that perpendicular force can be different in different cases. Pressure due to solids and liquids is usually due to the force of gravity. Pressure in gases is due to collisions by gas molecules.
The key question is this: how can we calculate pressure and thus the forces on an object in a ...