Sound

This lesson covers: 

  1. The properties of longitudinal waves
  2. How sound travels through a medium
  3. Reflection and absorption of sound
  4. Factors affecting the speed of sound
  5. Frequency as a measure of sound pitch

Sound is a longitudinal wave

Diagram showing particle movement and direction of energy transfer in a longitudinal wave.

Longitudinal waves have vibrations that are parallel to the direction of wave travel.

Examples of longitudinal waves include sound waves and slinky springs when they are compressed and released.

Sound is a pressure wave

Diagram showing sound wave compressions and rarefactions with particle movement.
  • Sound is generated by vibrating particles.
  • It requires a medium like air or water to travel through, as it is the movement of the particles that transmits the vibrations.
  • The vibrations pass through the medium as alternating compressions and rarefactions.
  • Sound cannot travel through a vacuum because there are no particles to transmit variations.

Reflection and absorption of sound

Like light waves, sound waves can be reflected and absorbed.

Diagram showing the reflection and absorption of sound waves with examples of sound being reflected off a surface and absorbed by carpet.
  • Some materials reflect sound waves, producing echoes.
  • Soft materials like carpet, can absorb and dissipate sound energy.

Factors affecting the speed of sound

Diagram showing the speed of sound in gases, liquids, and solids with varying densities.
  • More dense media transmit sound faster because particles are closer together.
  • Generally, sound travels fastest in solids, slower in liquids, and slowest in gases.

Frequency and pitch

Diagram showing high frequency with high pitch and low frequency with low pitch.
  • Frequency measures how many waves pass a point per second.
  • High frequencies correspond to high-pitched sounds.
  • Low frequencies correspond to low-pitched sounds.
  • Frequency is measured in Hertz (Hz).