Traveling Between Materials Remember that sound travels faster in some materials than others. Sound waves travel outward in straight lines from their source until something interferes with their path. When sound changes mediums, or enters a different material, it is bent from its original direction. This change in angle of direction is called refraction.
Refraction is caused by sound entering the new medium at an angle.
Because of the angle, part of the wave enters the new medium first and changes speed. The difference in speeds causes the wave to bend. The angle of refraction depends on the angle that the waves has when it enters the new medium. As the angle from the wave to the barrier between the two mediums gets smaller, the angle of refraction also gets closer to the barrier. When the wave s entering angle reaches a certain point, called the critical angle, the refraction is parallel to the dividing line between the mediums.