BUY THE YEAR 9 PHYSICS WORKBOOK
Sound Waves
- Sound is a form of energy that is transferred as a wave.
- Sound waves are mechanical waves, which means they involve the vibration of particles.
- Therefore, sound can travel through solids, liquids and gases, but cannot travel through a vacuum.
- Sound waves are longitudinal waves, which means that sound is the result of particles vibrating back and forth – in line with the direction that the sound wave is travelling.
Sound waves involve longitudinal particle vibrations.
(Image: © Dan Russell)
Generation of Sound Waves
- Like all mechanical waves, sound waves require a source of vibration that disturbs the surrounding medium – such as air – which transfers the sound wave.
- Examples
- • Our voices are the result of vibration of our vocal cords.
- • Striking a drum generates sound by vibrating the drum skin.
- • A piano generates sound when a hammer connected to a key strikes a string.
- • A speaker generates sound due to electrical signals that cause it to vibrate back and forth.
Speakers generate sound waves by disturbing the surrounding air.
Compressions and Rarefactions
- Since sound waves involve the movement of particles back and forth, they result in regions where particles are closer together and regions where particles are further apart.
- For sound waves travelling through air, these are alternating regions of higher and lower air pressure.
- The regions of higher pressure are called compressions.
- The regions of lower pressure are called rarefactions.
Sound waves involve alternating compressions and rarefactions.
(Image: © Dan Russell)
(Header image: Thaut Images, Adobe Stock)