turin said:You can think of it as the average of what the molecules are doing there. The compression peaks occur where the molecules are coming together, so the displacements of the molecules are all directed towards that point and they average out to zero. Similarly for rarefaction, except that they are direcected away from that point.
A longitudinal wave is a type of wave in which the particles of the medium vibrate in the same direction as the direction of the wave's motion. This type of wave is also known as a compression wave because the particles are compressed and expanded as the wave passes through them.
Compression or rarefaction at displacement 0 is determined by the position of the particles in the medium when they are at rest. At displacement 0, the particles are neither compressed nor expanded, and are in their equilibrium position. This point is also known as the zero displacement point.
Compression is the region of a longitudinal wave where the particles are close together, while rarefaction is the region where the particles are spread apart. This is due to the alternate compression and expansion of the particles as the wave passes through them.
The wavelength of a longitudinal wave is the distance between two consecutive points of compression or rarefaction. A shorter wavelength means that the compression and rarefaction regions are closer together, while a longer wavelength means they are farther apart.
Some examples of longitudinal waves include sound waves, seismic waves (such as P-waves), and pressure waves in fluids. Longitudinal waves can also be observed in springs, where the particles of the medium (the coils) vibrate back and forth in the same direction as the wave's motion.