Summary and Main Ideas

Summary

• Sound waves are longitudinal waves

• The frequency of a sound is an indication of how high or low the pitch of the sound is.

• The human ear can hear frequencies from 20 to \(\text{20 000}\) \(\text{Hz}\). Infrasound waves have frequencies lower than \(\text{20}\) \(\text{Hz}\). Ultrasound waves have frequencies higher than \(\text{20 000}\) \(\text{Hz}\).

• The amplitude of a sound determines its loudness or volume.

• The tone is a measure of the quality of a sound wave.

• The speed of sound in air is around \(\text{340}\) \(\text{m·s$^{-1}$}\). It is dependent on the temperature, height above sea level and the phase of the medium through which it is travelling.

• Sound travels faster when the medium is hot.

• Sound travels faster in a solid than a liquid and faster in a liquid than in a gas.

• Sound travels faster at sea level where the air pressure is higher.

• The intensity of a sound is the energy transmitted over a certain area. Intensity is a measure of frequency.

• Ultrasound can be used to form pictures of things we cannot see, like unborn babies or tumours.

• Echolocation is used by animals such as dolphins and bats to “see” their surroundings by using ultrasound.

• Ships use sonar to determine how deep the ocean is or to locate shoals of fish.

Table: Units used in sound