Sound waves are longitudinal waves with rarefaction and compression.

As an object’s vibration moves toward air it creates a compression

As the object moves away from air it creates a partial vacuum (rarefaction)

Sound travels faster through solids and liquids than through air.

Sound can only travel as fast as the air molecules. (about 340 m/sec)

Q: Will sound travel faster in hot or cold air? (Why?)

The amplitude of a sound wave (the amount of compression) determines the loudness of the sound.

Loudness is measured in decibels (dB).

Whisper 20 dB

Loud conversation 60-70 dB

Loud music 90-100 dB (hearing damage starts)

Jackhammer 120 dB (pain starts)

The wavelength (or frequency) of a sound wave determines the pitch. The higher the frequency the shorter the

wavelength (more energy)

High frequency

Low frequency

wavelength

wavelength

Doppler effect – the change in pitch resulting from a moving sound source (like a siren moving past you)

• The frequency changes as an object moves past you.

• Higher pitch – moving towards you

• Lower pitch – moving away from you

When something moves faster than sound, sound waves pile up and create a shock wave. (sonic boom)

Shock Wave

Sonar – uses the time it takes for a sound wave to bounce back to determine distance. (a depth finder)

Echolocation uses sonar to locate object (Dolphins, whales and bats use echolocation)