Why does sound intensity decrease with distance?

Sound intensity decreases with distance because it spreads out and disperses over a larger area as it travels away from its source.

Sound is a type of energy that travels in waves. When a sound is produced, it radiates outwards from the source in all directions. This is similar to the ripples created when a stone is thrown into a pond. The energy of the sound wave is spread over an increasingly larger area as it moves away from the source. This spreading out, or dispersion, of the sound wave leads to a decrease in the sound intensity, or loudness, that is perceived.

This phenomenon is known as the inverse square law. The inverse square law states that the intensity of a sound is inversely proportional to the square of the distance from the source. In simpler terms, if you double the distance from the sound source, the intensity of the sound is reduced to a quarter of its original value. If you triple the distance, the intensity is reduced to a ninth, and so on.

This is why, for example, a loud concert or a noisy construction site can be clearly heard from close by, but as you move further away, the sound becomes less and less loud. It's not that the sound is getting weaker, but rather that its energy is being spread over a larger and larger area, reducing the intensity of the sound that reaches your ears.

In addition, sound waves can also be absorbed or reflected by objects in their path, which can further reduce the intensity of the sound. For example, sound waves can be absorbed by soft materials like carpet or curtains, and reflected by hard surfaces like walls or floors. This is why soundproofing a room often involves using materials that can absorb or reflect sound waves, to reduce the amount of sound that escapes from the room.