Sound Waves and Ultrasound

This lesson covers sound waves, how they are produced and detected, the limits of human hearing, and the uses of ultrasound, as required by the AQA GCSE Physics specification (4.6.1). Sound is a longitudinal wave that requires a medium to travel through and has many practical applications in medicine and industry.

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How Sound Is Produced

Sound is produced when an object vibrates. The vibrations cause the particles of the surrounding medium (usually air) to vibrate, creating a series of compressions and rarefactions that travel outward as a longitudinal wave.

Examples of vibrating objects that produce sound:

Source	Vibrating Part
Guitar	Strings vibrate
Drum	Drum skin vibrates
Tuning fork	Prongs vibrate
Loudspeaker	Cone vibrates
Human voice	Vocal cords vibrate

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Properties of Sound Waves

Sound waves are longitudinal waves:

• The particles of the medium vibrate parallel to the direction of energy transfer.
• Sound waves consist of alternating compressions (high pressure) and rarefactions (low pressure).
• Sound waves require a medium to travel through — they cannot travel through a vacuum.