Summary
Pressure is the force spread over an area: the same force makes more pressure the smaller the area, which is why a sharp knife cuts better. It is measured in pascals (Pa). Liquids and gases, that is, fluids, exert pressure on everything they touch.
Inside a liquid, pressure increases with depth: that is why your ears hurt when diving. Air also has weight and exerts atmospheric pressure on us. There are two important principles: Pascal's, which explains how pressure is transmitted inside a liquid (a car's brakes), and Archimedes', which explains why objects float: a submerged body receives an upward push equal to the weight of the liquid it displaces.
Key points
- Pressure is force spread over an area; it is measured in pascals (Pa).
- The smaller the area, the more pressure with the same force.
- Fluids (liquids and gases) exert pressure on what they touch.
- In a liquid, pressure increases with depth.
- Atmospheric pressure is the pressure the air exerts on us.
- Pascal's principle: pressure is transmitted in a liquid (hydraulic brakes).
- Archimedes' principle: a submerged body gets an upward push (floating).