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 atmospheric pressure is exactly 1 atm, the boiling point of water is 100.0 degrees Celsius. This is because the vapor pressure of water is 1 atm at this temperature. If you increase the pressure, the boiling point will increase because more energy will be needed to raise the vapor pressure to the increased atmospheric pressure. Likewise, if you decrease the pressure, the boiling point will decrease.