Longitudinal Waves. To see a animations of spherical longitudinal waves check out: In a longitudinal wave the particle displacement is parallel to the direction of wave propagation. The animation at right shows a one-dimensional longitudinal plane wave propagating down a tube.
The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.
If the pressure of a gas is held constant, its volume is proportional to the temperature. As the temperature increases, the atoms move faster and require more space so that they strike the walls of the container with the same net force. The volume increases. If the temperature of a gas is held constant, its pressure is inversely proportional to the volume. If the volume of a gas is decreased, then the same number of atoms moving at the same speed (because the temperature has not changed) will strike the walls of the container more often.