Physics - Pressure 3.04

1. Liquids and gases are fluids 

 

Liquids and gases are fluids. 

Molecules or particles can move around freely in fluids. 

Solids are not fluids. 

The particles in solids can only vibrate around a fixed position. 

 

 

 

1. Fluids exert forces on objects they touch 

 

If an object is placed in a fluid, the fluid's particles constantly collide with it. 

As a result, the fluid is exerting a force on the object. 

 

 

The force is normal (at right angles) to any surface touching the fluid. 

The force acts over the area of the surface, creating pressure. 

So the pressure at a point in a gas or liquid at rest acts equally in all directions. 

You can calculate the pressure at the surface using this equation: 

 

 

1. Air pressure is all around us 

 

The thin layer of air surrounding the Earth is called the atmosphere. 

When air molecules hit different surfaces they exert a force. 

This force…