Chapter 13: Sound and Waves

Air Pressure Pressure: a measure of the force felt by the walls of the container holding the gas More molecules = more pressure High pressure in a wave would be shown at its crest Low pressure in a wave would be show at its trough Sound waves are longitudinal Sound DOES NOT travel in space!! Science fiction movies add sound to make it more interesting, but there is not air in space to carry sound waves

Loudness of Sound Decibel: the unit that we use to measure sound Whisper – 10 dB Conversation – 65 dB City traffic – 70 dB Construction – 90 dB Rock concert – 110 dB

Sensitivity of the Ear You ears can detect a change in pressure of less than 1 in a million Because our ears are so sensitive, loud sounds can damage our hearing easier Different places work to absorb sound so that it does not both us (libraries, recording studios, etc) Acoustics: the science and technology of sound

Frequency of Sound You hear different frequencies of sounds, the pitch will change Truck has low frequency – we hear it rumbling next to us Whistle has high frequency – it is sharper and sounds louder to us Most sounds have more than one frequency Sonogram: shows how loud sound is at different frequencies White noise: an equal mixture of all frequencies There is not a pattern the brain can recognize, so for some people it is relaxing White noise is similar to the static on a television

Wavelength of Sound Frequency (Hz)WavelengthTypical Source 2017 metersRumble of thunder metersBass guitar cmAverage male voice 1,00034 cmFemale soprano singer 2,00017 cmFire truck siren 5,0007 cmHighest note on piano 10, cmWhine of a jet turbine 20, cmHighest pitched sound you can hear

Speed of Sound Under average conditions, the speed of sound is about 660mph Supersonic: when motion is faster than sound