Properties of Sound

Definition

Sound is a longitudinal mechanical wave produced by vibrating bodies that travels through a material medium by compressions and rarefactions.

Key points

• Sound needs a medium and cannot travel through a vacuum; it travels fastest in solids, slower in liquids, and slowest in gases (about 343 metres per second in air at room temperature).
• Pitch depends on frequency (higher frequency means higher pitch), and loudness depends on amplitude; loudness is measured in decibels.
• The audible range for humans is roughly 20 hertz to 20,000 hertz; sound below 20 hertz is infrasound and above 20,000 hertz is ultrasound.
• An echo is the reflection of sound; reverberation is the persistence of sound due to repeated reflections in an enclosed space.
• The speed of sound rises with temperature in air, and unlike light, sound bends (refracts) less and is much slower, which is why thunder is heard after lightning is seen.

Why it matters for CAPF

The need for a medium, the relative speed in solids, liquids, and gases, the audible range, infrasound and ultrasound, and echo versus reverberation are standard physics facts that appear regularly.

Common confusion

Sound cannot travel in vacuum, while light can; pitch is set by frequency and loudness by amplitude, so a high-pitched sound is not necessarily loud. Sound travels fastest in solids, not in air, which is the opposite of the everyday intuition.

Related concepts

concept ultrasound and sonar, concept doppler effect, concept electromagnetic spectrum

Parent note

physics everyday