A vibrating tuning fork is capable of creating longitudinal waves. When the fork is hit on something the tines of the fork vibrate back and forth. This causes the tines to push on neighboring air particles. The forward motion of a tine pushes air molecules horizontally to the right and the backward retraction of the tine creates a low pressure area allowing the air particles to move back to the left. Because of the longitudinal motion of the air particles, there are regions in the air where the air particles are compressed together. This causes other regions of air particles to spread apart. The two different regions are known as compressions and rarefactions. The compressions are regions of high air pressure. While, on the other hand, rarefactions are regions of low air pressure.