Why is sound wave called a longitudinal wave?

A sound wave earns the title of a “longitudinal wave” due to the distinctive manner in which it navigates through a medium. Longitudinal waves are characterized by particle movements aligning parallel to the wave’s direction of travel.

When we consider a sound wave:

1. Particle Movement: Picture the sound traveling through air. The particles in the air sway to and fro along the same axis as the wave’s journey. This means that as the sound wave moves forward, the particles of air move back and forth in a parallel manner to the wave’s motion.

2. Compression and Rarefaction: As the sound wave progresses, it generates areas of high pressure called compressions and areas of low pressure known as rarefactions. Within these zones, the air particles experience sequences of being pushed closer together (compression) and then stretched farther apart (rarefaction) along the path of the sound wave.

The movement of particles within a longitudinal wave resembles the motion of a slinky when you push one end back and forth—each coil moves along the same line as the wave moves through the slinky.

In contrast, a transverse wave involves particles oscillating perpendicular to the direction of the wave’s travel. Imagine a wave traveling along a rope where the particles move up and down while the wave moves horizontally.

Therefore, a sound wave’s classification as a longitudinal wave stems from the fact that the particles oscillate in a parallel fashion to the direction in which the sound wave traverses through the medium.