Sound is a vibration that travels through a medium like air or water.

Sound waves are longitudinal waves.

The speed of sound depends on the medium (faster in solids, slower in gases).

Humans hear sounds between 20 Hz and 20,000 Hz.

Ultrasound uses sound waves with frequencies higher than humans can hear.

Echoes occur when sound reflects off surfaces.

The loudness of sound is measured in decibels (dB).

Pitch depends on the frequency of the sound wave.

Animals like bats use echolocation to navigate using sound.

Sound cannot travel in a vacuum because there is no medium.