http://www.ck12.org Chapter 5. Energy
FIGURE 5.48
Compressions and Rarefactions
Notice in theFigure5.48 that the coils of the spring first crowd closer together and then spread farther apart as the
wave passes through them. Places where particles of a medium crowd closer together are called compressions, and
places where the particles spread farther apart are called rarefactions. The more energy the wave has, the closer
together the particles are in compressions and the farther apart they are in rarefactions.
P Waves
Earthquakes cause longitudinal waves called P waves. The disturbance that causes an earthquake sends longitudinal
waves through underground rocks in all directions away from the disturbance. P waves are modeled in theFigure
5.49.
FIGURE 5.49
Q:Where are the compressions and rarefactions of the medium in this model of P waves?
A:The compressions are the places where the vertical lines are closest together. The rarefactions are the places
where the vertical lines are farthest apart.
Summary
- A longitudinal wave is a type of mechanical wave, or wave that travels through matter, called the medium. In
a longitudinal wave, particles of the medium vibrate in a direction that is parallel to the direction that the wave
travels.