9.04 Sound Waves

Sound

Sound waves are longitudinal waves. When a sound is made:

• The molecules in the medium are compressed together and pulled apart by the vibrations of its origin.
• These waves travel through the medium, such as air, by vibrating the molecules in the matter which produces the sound. Sound waves can also travel through solids and gases. (Because sound waves require a medium to travel, they are also mechanical waves.)

The size of the compressions and the distance between them determines the nature of the sound.

The loudness is determined by the size of the wave. The speed of a wave is determined by the medium through which it travels.

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Speed of Sound

Sound can travel four times faster and farther in water than it does in air. This is because of the spacing of the molecules in a liquid are closer than those of a gas. Since the molecules of a solid are closer than a liquid, sound waves can travel faster through the solid than the liquid.

An increase in temperature increases the speed in which sound can travel through a material. As the temperature increases, the molecules of the material move faster. This makes them more likely to collide with each other. If the particles that make up a medium collide more often, more energy can be transferred in a shorter amount of time. This results in the sound traveling faster.

Material	Speed (m/s)
Air (0°)	330
Air (20°)	340
Cork	500
Water (0°)	1,400
Water (20°)	1,500
Copper	3,600
Bone	4,000
Steel	5,800

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Properties of Sound Energy

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How Sound Travels: Transmission, Reflection, and Absorption

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