Liquids and gases are called fluids, and one of their most important properties is that they exert pressure on the surfaces around them.
Unlike solids, which usually exert pressure in one direction (downwards), fluids exert pressure in all directions.

1. Fluids exert pressure in all directions

When a fluid (like water or air) touches the walls of a container, it pushes:

  • sideways

  • upward

  • downward

This is why:

  • a balloon expands from all sides when air fills it

  • water leaks from holes on any side of a bottle

  • deep-sea divers feel pressure from all directions

This shows fluid pressure acts in every possible direction.

2. Pressure increases with depth (in liquids)

The deeper you go underwater, the greater the pressure.
This happens because water above you creates more weight, and that weight pushes down.

Examples:

  • A swimmer feels more pressure when diving deeper.

  • The bottom of a dam is built thicker and stronger to handle high water pressure.

  • Submarines have strong metal bodies to survive huge pressure at great depths.

So, depth increases water pressure.

3. Pressure in gases (air pressure)

Gases also exert pressure.
Air around us pushes on everything and creates atmospheric pressure.
This is why:

  • we can use suction cups

  • drinking through a straw works

  • balloons expand when filled

Air pressure plays a major role in weather, flying airplanes, and many machines.

4. Applications of fluid pressure

✔ Dams

Dams are built thicker at the bottom because the lower part faces more water pressure.

✔ Submarines

Submarines are designed with strong outer shells so they don’t get crushed under high water pressure deep in the ocean.

✔ Hydraulic brakes

Hydraulic systems (in cars, machines, etc.) use liquids to transfer pressure.
When a small force is applied on one end, the liquid transfers it and creates a much larger force at the other end.

This is why a small push on the brake pedal can stop a heavy car.

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