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We use Particle Theory to explain many things in Science. The basics look at how the particles are arranged in a solid, liquid and a gas.
Properties of solids, liquids and gases
When we move between the three states of matter, we are said to change state.
We need to know the names of the changes of state for moving between the following..........
Solid to liquid - melting
Liquid to solid - freezing
Liquid to gas - evaporation (can occur at any temperature) or boiling (can only occur above the substance's boiling point
Gas to liquid - condensation
Solid to gas - sublimation (this one is very rare and not many things go straight from a solid to a gas. Examples include iodine and carbon dioxide)
Because gas particles are constantly moving around in random directions and at high speed, they are constantly colliding into objects. When they collide into an object, they exert a 'force'.
The force that is exerted over a given area is called the 'gas pressure', or you will sometimes see it called the 'air pressure' if it is referring to the air around you.
Remember from Physics and Mathematics that;
Pressure = force / area
Because the common unit of force is Newtons (N) and the common way that area is described is m2, we commonly give the units of pressure as...
N / m2
A pressure of 1 N / m2 is commonly called 1 Pascal (or 1 Pa)
As a little side fact, the average pressure exerted by the air particles around you right now, at sea level, is about 101,000 Pa. That means the air is exerting a force of 101,000 N for every m2 area... impressive stuff!
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