Pressure in Fluids, Upthrust & Archimedes’ Principle — A/L Physics

Fluid Pressure The force exerted per unit area by a fluid at rest, acting perpendicular to any surface in contact with it. Pressure in a fluid arises from the weight of the fluid above the point. It increases linearly with depth because the weight of the overlying fluid column increases. Unlike solids, fluid pressure acts equally in all directions at a given depth. For example, a dam is built thicker at the bottom because water pressure is greatest there.

Pascal’s Principle When an external pressure is applied to an enclosed fluid, it is transmitted undiminished to every point in the fluid and to the walls of the container. This principle is the basis for hydraulic systems. A small force applied over a small area creates a pressure that is transmitted to a larger area, producing a larger force. A car hydraulic jack uses this: a small piston force lifts a heavy vehicle because the pressure is the same on both pistons.