A tuning fork consists of two metal prongs, or tines that vibrate when struck. The vibrations of these tines disturb the air near them. When a wave approaches a boundary or obstacle which is in its path, it can behave in a number of ways. Three common behaviors include reflection, refraction, and diffraction. Reflection is the wave that bounces off of something that might not always be in the same direction.
Refraction is the effect on a wave when there are changes in a medium.
Diffraction is the bending of waves around an object in its path. The motion of the medium particles in a longitudinal wave is back and forth along the direction in which the wave travels. This is in contrast to a transverse wave, in which the vibrations of the medium are at right angles to the direction of the travel of the wave. The general motion of air molecules near a vibrating object is such that they move back and forth between regions of compression and rarefaction. Sound waves are key to understanding the properties of sound and its characteristics.