In the last segment, we learnt that sound cannot propagate through a vacuum. In this segment, we are going to learn that sound waves are longitudinal waves.
The waves can be classified into types based on the vibration of the particles: Longitudinal waves and Transverse waves.
What are Longitudinal Waves?
Waves in which the particles of a medium vibrate, in a direction parallel or antiparallel to the direction of energy transport or wave propagation, are called longitudinal waves.
It means that if the source is emitting sound in a particular direction, then the particles of the medium also move to and fro along the same direction only. So the displacement of particles is parallel or antiparallel to the direction of the propagation of the wave.
Longitudinal Wave
 Example: Longitudinal Wave
Sound waves are longitudinal waves because the particles of the medium vibrate in the direction of the propagation of the sound wave.
Sound waves are also called pressure waves. It is because the sound wave consists of the
repeating pattern of high-pressure regions called compressions, and low-pressure regions called rarefactions through the medium.
What are Transverse Waves?
Waves in which the particles of a medium vibrate, in a direction perpendicular to the direction of energy transport or wave propagation, are called transverse waves.
Transverse Wave
Example: Transverse Wave
Take a string with one end fixed to the wall. We will see a wave is formed on giving the string an upward jerk. You will observe that the particles in the string are moving up and down while the direction of propagation of the wave is towards the right. The particles are vibrating in a direction perpendicular to the direction of a wave.