Longitudinal acoustic wave

Professional Definition

A longitudinal acoustic wave is a wave in which the direction of particle vibrations in the medium is in line with the direction in which the wave propagates.

This means that the velocity vector of the particles is parallel to the direction in which sound travels. This mechanism involves the formation of successive local compressions and rarefactions of the medium. In fluids such as gases (air) and liquids (water), which do not carry shear stresses, sound can only propagate as a longitudinal wave.

Acoustics in Simple Words

The best analogy for a longitudinal wave is a "Slinky" spring (a colorful toy that can "walk" down stairs).

If you stretch such a spring on a flat surface and suddenly push one end towards the other, you will see a "bunch" of tightly coiled loops that swiftly move along the spring. The coils vibrate back and forth – exactly in the same line along which the impulse travels.

Similarly, air behaves: when a speaker's diaphragm moves out, it hits the closest air particles, and these push their neighbors. A chain of collisions is formed that reaches your ear. No particle flies from the speaker to you – they merely transfer energy by "nudging" each other along the path of sound travel.

Summary

• Direction of vibrations: Particles move "back and forth" along the line of travel of the wave.

• Pressure changes: This type of wave is responsible for changes in atmospheric pressure that our ears interpret as sound.

• Ubiquity: This is the fundamental and only way in which sound travels through the air.