Pressure

Learning objectives

To illustrate the behavior of gas molecules.
To link the pressure of a gas and the number of collisions with the wall of the container per unit of time.
To introduce the relationship between volume and pressure.
To avoid confusing pressure (a scalar quantity) and force (a vector quantity).
To define the units of pressure (Pa, mb, atm).

Pressure is directly tied to the microscopic behavior of matter. Gas molecules collide with one another continuously. The mass of any single molecule is extremely small, but they are so numerous that collisions with the walls exert a force that pushes on those walls. Pressure is the expression of this force per unit of surface area.

The smaller the volume, the more numerous are these collisions, and the greater the resulting pressure is.