  # Unit 3 Properties of waves

Notes

## Sound wave characteristics

• The speed of sound varies from material to material. A sound wave compresses (pushes together) and rarefies (spreads apart) the particles of the material, and how easily this happens affects the speed of the wave.
• Sound travels fastest in solids because the molecules in a solid are very close together.
• Sound travels second fastest in liquids because the molecules in a liquid are only slightly further apart.
• Sound travels slowest in gases because the molecules in a gas are far apart.
• Remember: Sound cannot travel through a vacuum because there are no particles.
• Some examples of the speed of sound in different media are given below.
• In dry air at 0°C the speed is 330m/s.
• In dry air at 20°C the speed is 340m/s.
• In water the speed is 1500m/s.
• In gold the speed is 3200m/s.
• In steel the speed is 5800m/s.
• Frequency, pitch, wavelength and amplitude are terms associated with sound waves.
• Frequency is the number of wavelengths produced per second and its unit is the hertz (Hz).
• Pitch is how high or low a sound is and is dependent on frequency.
• Wavelength is the distance from any point on one wave to the same point on the adjacent wave. Its unit is the metre (m).