A sound wave is called a longitudinal wave because the particles of the medium through which the sound travels oscillate parallel to the direction of the wave propagation. In other words, the displacement of particles in a longitudinal wave is along the same line or axis as the direction of the wave.
Here’s a breakdown of the characteristics of longitudinal waves, including sound waves:
Particle Oscillation: In a longitudinal wave, the particles of the medium (solid, liquid, or gas) move back and forth in the same direction as the wave is traveling. This back-and-forth motion is referred to as oscillation.
Compression and Rarefaction: Within a longitudinal wave, regions of compression and rarefaction alternate. During compression, particles are pushed close together, resulting in a region of higher pressure. In rarefaction, particles are spread apart, leading to a region of lower pressure.
Wave Motion: The disturbance caused by the source of the wave (such as a vibrating object in the case of sound waves) travels through the medium by causing adjacent particles to oscillate. This creates a wave pattern where the disturbances are propagated along the same axis as the particle oscillations.
Sound Waves: In the case of sound waves, the source of the sound, such as a vibrating object like a drum membrane or vocal cords, creates compressions and rarefactions in the surrounding air particles. These pressure variations then travel through the air, and our ears perceive them as sound.
The opposite of a longitudinal wave is a transverse wave, where particle oscillation is perpendicular to the direction of wave propagation. Light waves are an example of transverse waves, where the electric and magnetic fields oscillate perpendicular to the direction of the wave.
In summary, sound waves are called longitudinal waves because the particles of the medium move parallel to the direction in which the sound wave travels. This characteristic distinguishes longitudinal waves from transverse waves, where particle oscillation is perpendicular to the wave direction.