What is the difference between longitudinal and transverse waves?

Waves can be characterized as either longitudinal or transverse waves. The major difference between the two types of waves is in terms of the direction of propagation of wave relative to the displacement of medium. If the displacement of the medium is parallel to the direction of wave propagation, such waves are known as longitudinal waves. If, on the other hand, the displacement of medium is perpendicular to the direction of wave propagation, the waves are classified as transverse waves. In the case of longitudinal waves, such as sound waves, we have regions where molecules are close together (known as compressions) and regions where molecules are far apart (known as rarefactions). In the case of transverse waves, such as those generated on a rope or ripples on water surfaces, we use terms such as crests and troughs to define the displacement from the center line. Transverse waves, unlike longitudinal waves, cannot take place in fluids (gas or liquid phases).

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