Fluids - Introduction
A fluid is any substance that can be poured or that can flow:
These are generally the two states of matter that can be classified as fluids.
As we know from the Particle Theory of Matter, Gases can be compressed fairly easily into smaller volumes.
This is because the particles of a gas have large spaces between them and any external pressure will cause the particles to move into smaller spaces, thus occupying a smaller volume.
Liquids can also be compressed but to a much lower extent than gases. The spaces between particles of liquids are not as large as those separating particles of gases.
Solids cannot generally be compressed at all and if external pressure is applied to a solid it will discrupt the sturcture of its particles and, depending on the amount of pressure applied to it, and the type of solid and its structural characteristics, coud cause the solid to either deform or collapse (crack).
Vapours are a special class of gases. A vapour is generally defined as the gaseous state of a substance, which at room temperature is usually in its liquid state.
When we refuel our cars at the gas pump, we smell the strong smell of gasoline. On a hot day the smell is even stronger. Why?
Gasoline is a very volatile liquid. This means that it easily evaporates even at lower temperatures and/or at room temperature. As the temperature increases the motion of the partices of the liquid increase (Kinetic Molecular Theory) and their rate of diffusion also increases, therefore the gasoline evaporates faster and the smell is stronger.