Refraction, or bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves. Thus waves passing from one medium to another will undergo refraction. Refraction of sound waves is most evident in situations in which the sound wave passes through a medium with gradually varying properties. For example, sound waves are known to refract when traveling over water. Since water has a moderating effect upon the temperature of air, the air directly above the water tends to be cooler than the air far above the water.
Sound waves travel slower in cooler air than they do in warmer air.
For this reason, the portion of the wavefront directly above the water is slowed down, while the portion of the wavefronts far above the water speeds ahead. Subsequently, the direction of the wave changes, refracting downwards towards the water. This is depicted in the diagram at the right. Refraction of other waves such as light waves will be discussed in more detail in a later Unit 14 of The Physics Classroom .