The energy of a sound wave typically decreases over time due to a phenomenon called "attenuation." Attenuation refers to the gradual loss of energy as sound propagates through a medium, such as air or water. There are several factors that contribute to sound wave attenuation:
Geometrical spreading: As a sound wave travels outward from its source, it spreads out in a spherical or cylindrical shape, depending on the environment. The spreading of the wavefront leads to a decrease in the intensity (power per unit area) of the sound wave, resulting in a reduction of energy.
Absorption: The medium through which the sound wave travels can absorb some of its energy. Different materials have varying abilities to absorb sound waves. For example, soft and porous materials like foam or fabric tend to absorb more sound energy compared to hard surfaces like metal or glass.
Scattering and reflection: When sound encounters an obstacle or an irregular surface, such as a wall or an uneven object, it can scatter or reflect in different directions. Some of the sound energy is redirected away from the original path, leading to a decrease in the overall energy of the sound wave.
Viscous and thermal losses: In certain media, such as air, the interaction of sound waves with the molecular structure of the medium causes energy losses due to viscosity and thermal effects. These losses result in the conversion of sound energy into heat, leading to a gradual decrease in the sound wave's energy.
It's important to note that the rate of energy loss and the distance over which sound energy decreases can vary depending on factors like the frequency of the sound wave, the properties of the medium, and the environmental conditions.