In longitudinal waves,<span> the disturbance of the medium is in the same or opposite direction to the wave's propagation direction. If the medium is mechanical, the longitudinal wave is also called c</span>ompression wave<span> because it produces compression and </span>rarefaction<span> when traveling through.</span>
Sound waves are both compressional and longitudinal, (although we frequently draw them as transverse waves).
Longitudinal waves are where the particles of matter collide into one another, pushing them into the next and then oscillating back. This is how sound travels. This is also why sound can only travel through a medium, it cannot travel through a vacuum, as is shown here:
