Each of following diagrams shows a simplified picture of the air molecules in front of a loudspeaker before and after it was
turned on.
Sound waves in air are longitudinal because the particles oscillate parallel to the direction of propagation. A way to describe the above sound wave is in terms of the displacement of the particles at different positions from the loudspeaker.
Another way is in terms of the variation in air pressure at different positions.
As a sound wave passes through air, a series of alternating high (compressions) and low (rarefactions) air pressure regions propagate forwards. Sound has all the properties of a wave, namely reflection, refraction, diffraction and interference. An example of refraction of sound is when it travels from a region into another region of different temperature. Sound travels faster in a warmer region (longer l ) than in a cooler region (shorter l ), and it bends towards the normal, i.e. Ði > Ðr.
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