Compressional waves are waves that move along the direction of propagation in a back and forth motion. Common examples of compressional waves include sound waves and P waves, which are types of seismic waves.
Waves are generally defined as disturbances that occur along a medium and are characterized by their wavelengths, frequencies and periods. Waves are broadly categorized into three types: mechanical, electromagnetic and matter. Mechanical waves require a medium, typically solid, liquid or gaseous materials, for their propagation. Electromagnetic waves can travel through space and vacuums, while matter waves naturally occur within atomic particles.
Mechanical waves involve particle motions due to the inherent properties of matter, such as inertia and elasticity. Some examples of wave motions along a material include vibrations, oscillations and tremors. The two types of mechanical waves based on the direction of wave propagation are called longitudinal and transverse. Longitudinal waves are parallel to the direction of propagation, while transverse waves are perpendicular to the direction of propagation. Longitudinal waves are also referred to as compressional waves.
Compressional waves are composed of alternating compressions and rarefactions. Pressure levels and densities are at their highest at areas of compression, while they are at their lowest at areas of rarefaction. The media by which compressional waves travel tend to return to their original shapes once the waves pass. Other examples of compressional waves include tsunami waves, ultra sounds, gas vibrations, spring oscillations and slink waves.