1. Behaviour of Fluids
Chapter 3

2. What is Fluid?
A Fluid is a substance that has the capacity to flow and assume the form of the container into which it has been poured. A Fluid can be either a liquid or a gas.
Therefore a Fluid will
Assume the shape
Are 100% adaptable

3. Flow and Deform
The capacity for a fluid to flow or deform can be explained using the Particle Model.

4. Liquids
Particles in a liquid are close together and are held together by forces of attraction that are relatively weak. This helps the particles to slide over each other and take the form of the container.

5. Gases
Particles of gas are much farther apart and are not bound together by forces of attraction. They move in every direction and occupy all available space.

6. Characteristics of a Fluid
Mixtures in a liquid or gaseous phase that contain solids but are able to flow are considered to be a fluid.
Gels and pastes are more difficult to identify. If they can flow and take on the form of their container then they are fluids.
Tiny pieces of a solid that are thought to flow (sand) are NOT considered a fluid.

7. Types of Fluids There are two types of Fluids:
Compressible fluids (gases)
Incompressible fluids (liquids)

8. Compressible Fluids
Compressible Fluid is a fluid whose volume can change in response to a change in pressure. Gases are compressible fluids.
Under pressure (or when pressure is released), particles will redistribute themselves evenly in what’s left of the available space.

9. Volume of a Compressible Fluid

10. Incompressible Fluids
An Incompressible fluid is a fluid whose volume cannot be varied. Liquids are incompressible fluids.
The particles in a liquid are already very close together and so applying pressure does not change the volume of the fluid.

11. Volume of an Incompressible Fluid

12. The particles in compressible and incompressible fluids are organised differently, each fluid exerts pressure in different ways.
Understanding the difference between compressible and incompressible fluids is essential for a thorough understanding pressure.