Compression and rarefaction are two concepts related to the behavior of waves, especially sound waves.
Compression refers to the region of a wave where the particles of the medium through which the wave is travelling are closer together than their average or rest position. This results in a region of high pressure and density, as the particles are tightly packed together. In a sound wave, compression is experienced as the high-pressure part of the wave, where the air molecules are crowded together.
Rarefaction, on the other hand, refers to the region of a wave where the particles of the medium are further apart than their average or rest position. This results in a region of low pressure and density, as the particles are more spread out. In a sound wave, rarefaction is experienced as the low-pressure part of the wave, where the air molecules are more spread out.
In summary, compression and rarefaction are two opposing regions of a wave that are characterized by high pressure and low density (compression) and low pressure and high density (rarefaction), respectively. These concepts are important in understanding the behavior of waves, especially sound waves, and are key to understanding many of their properties, such as frequency, wavelength, and amplitude.