Ever wondered how a fluid flows from one point to another? To understand this, consider a fluid of constant density at rest. If a force is applied parallel to the surface of the fluid, then to accommodate this force, the fluid is set into motion. In contrast, if a normal force is applied on the fluid's surface, an equal and opposite force develops in the fluid as a reaction. This normal force exerted by the fluid per unit area is called pressure. The SI unit of pressure is pascal. Pressure is always normal to any surface in contact with the fluid and so is a scalar quantity. In comparison, force has a specific direction and is a vector quantity. The pressure at a depth h from the fluid's surface is the sum of atmospheric pressure and pressure due to the fluid's weight. When we substitute the equivalent expressions for weight, mass, and volume, we get the pressure due to the fluid's weight as the product of density, acceleration due to gravity, and h.