Longitudinal waves are produced when the vibration which is transmitted and the propagation go in the same direction.

A good example of this type of phenomenon is the transmission of sound through a fluid. If you put your hand in front of your mouth as you talk you will notice how the air hits your hand when its particles vibrate in the same direction as the one in which your words are carried.

However, the easiest example to visualise is the oscillations which are transmitted along a spring. In the following visual we will study simultaneously the movement of the sound waves in the air and the transmission of longitudinal oscillations along a spring.