Chapter summary

The whole chapter in one list, and one graph.

• A disturbance that travels through a medium or through space is called a wave.
• Waves that need a material medium to travel are called mechanical waves.
• Waves that travel at right angles to the direction the particles of the medium move are called transverse waves.
• Waves that travel parallel to the direction the particles of the medium move are called longitudinal waves.

Amplitude is the height of a crest above the axis; the wavelength is the distance from one crest to the next.

• The time one particle takes to make one complete oscillation is the period.
• The number of oscillations one particle makes in unit time is the frequency.
• Electromagnetic waves need no material medium to travel.
• Sound waves are a kind of longitudinal wave, and sound needs a medium to travel.
• Pitch, loudness and quality are the three main characteristics of sound. Pitch depends on the frequency of the sound wave, loudness on its amplitude, and quality on the shape of its waveform.
• Regular vibrations make pleasant sounds, and irregular vibrations make noise.
• String instruments make sound when taut strings vibrate, wind instruments when a column of air vibrates, and percussion instruments when a stretched skin, a bar or a plate vibrates.
• Sound below 20 Hz is called infrasound, and sound above 20 000 Hz ultrasound.
• The range of frequencies an animal can hear is that animal's hearing range.