Waves - Sound

Sound is a longitudinal wave produced by vibrating sources that requires a medium (solid, liquid, or gas) to travel; it cannot travel through a vacuum.

Sound waves consist of compressions (regions of high pressure where particles are close together) and rarefactions (regions of low pressure where particles are spread apart).

The speed of sound depends on the medium: it is fastest in solids, slower in liquids, and slowest in gases (typically around $330 \text{ m/s}$ to $350 \text{ m/s}$ in air).

The pitch of a sound is determined by its frequency ($f$); a higher frequency results in a higher pitch.

The loudness of a sound is determined by its amplitude ($A$); a larger amplitude results in a louder sound.

The audible frequency range for a healthy human ear is approximately $20 \text{ Hz}$ to $20,000 \text{ Hz}$.

Ultrasound is defined as sound waves with a frequency higher than the upper limit of human hearing, i.e., greater than $20,000 \text{ Hz}$.

An echo is the reflection of sound waves from a surface. To calculate the distance to a surface using an echo, the sound travels a total distance of $2d$.