Final answer:
A sound wave causes alternating high and low pressure regions known as compressions and rarefactions as it passes through air. The intensity of the sound is proportional to the square of the pressure variation. The sound's amplitude, indicative of loudness, diminishes with distance from the source.
Step-by-step explanation:
When a sound wave propagates past a point in the air, the pressure of the air at this point experiences variations due to the alternating compressions and rarefactions created by the wave. As the sound source, such as a speaker or tuning fork, vibrates, it causes the air molecules to oscillate back and forth from their equilibrium positions, creating regions of high pressure (compressions) and low pressure (rarefactions). This results in a pressure wave that moves through the medium. These pressure variations, though typically slight compared to atmospheric pressure, are what constitute the sound wave and are detectable by the ear as sound.
The intensity of a sound wave is related to the square of the pressure variation; it also varies inversely with the density of the medium and the speed of sound within it. This relationship parallels the energy transmitted by the wave, which diminishes as the wave spreads out over a greater area and is partially absorbed or converted to thermal energy. The amplitude of the sound wave, which is the magnitude of the oscillation, determines the loudness of the sound and decreases with distance from the source, as a consequence of energy spreading and absorption.