Sound - Production and Propagation of Sound

Sound is a form of energy produced by vibrating objects. Vibration is the rapid to-and-forth motion of an object about its mean position.

In humans, sound is produced by the larynx (voice box). Two vocal cords are stretched across the larynx such that they leave a narrow slit for the passage of air; air expelled by the lungs makes the cords vibrate.

Sound requires a medium (solid, liquid, or gas) to propagate. It cannot travel through a vacuum because there are no molecules to compress and rarefy.

The speed of sound depends on the nature of the medium. Generally, $V_{solid} > V_{liquid} > V_{gas}$.

Amplitude ($A$) is the maximum displacement of a vibrating object from its central position. It determines the loudness of the sound. $\text{Loudness} \propto \text{Amplitude}^2$.

Frequency ($f$) is the number of oscillations per second, measured in Hertz ($Hz$). It determines the pitch or shrillness of the sound.

The time taken for one complete oscillation is called the Time Period ($T$). The relationship is $T = \frac{1}{f}$.

The audible range of frequencies for the human ear is roughly between $20\text{ Hz}$ and $20,000\text{ Hz}$.

Unpleasant sounds are termed as noise, while pleasing sounds are called music. Excessive or unwanted sound in the environment is called noise pollution.