What is Pressure?
Before diving into liquid pressure specifically, it helps to understand what pressure means in science.
The force acting per unit area on a surface. It is calculated as:
where is pressure (Pa), is force (N), and is area (m²).
The SI unit of pressure is the Pascal (Pa), where .
Think about walking on snow in normal shoes versus snowshoes. Your weight (force) is the same, but snowshoes spread it over a much larger area — so the pressure you exert on the snow is much less, and you don't sink. This is pressure in action!
Pressure can be exerted by solids, liquids, and gases. In this subtopic, we focus on liquids — and liquid pressure behaves in some fascinating and important ways.
How Liquids Exert Pressure
Liquids exert pressure because of gravity acting on their mass. The weight of the liquid above any point pushes down on the liquid below it, creating pressure.
This leads to one of the most important rules about liquid pressure:
Liquid pressure increases with depth. The deeper you go in a liquid, the greater the weight of liquid above you, and therefore the greater the pressure.
Unlike solids, liquids can flow and change shape. This means liquid pressure is exerted in all directions — not just downwards. At any point inside a liquid, the pressure acts equally in every direction: up, down, and sideways.
Imagine being underwater in a swimming pool. You feel the water pressing on your ears, your chest, your whole body — from all sides at once. That's because liquid pressure acts in all directions equally at the same depth.
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