Chapter 15 Sound

15.1 Properties of Sound Sound Waves longitudinal wave mechanical wave has properties similar to water reflection refraction diffraction interference

Produced by vibrating matter that cause the medium to have high pressure (compressions) and low pressure (rarefactions) speed depends upon ???? Speed of sound in air depends on the temperature of the air

331 m/s at 0o C for every 1o C the speed changes by 0.6 m/s goes up if temperature goes up and down if temperature goes down

Detection of Pressure Waves Sound detectors convert the KE of the vibrating matter into other forms of energy. Microphone- Sound KE into electrical energy Human ear- Sound pressure waves into electrical impulses

Perceiving Sound Pitch & Loudness Physical characteristics of sound waves are frequency amplitude

Humans detect sound with our ears Humans detect sound with our ears. Sound characteristics are defined in terms of what is perceived frequency is pitch amplitude is loudness

Marin Mersenne & Robert Hooke connected pitch with frequency Pythagoras musical scales are based on his work

Most people hear sound in the range of 20 Hz to 16,000 Hz Older people lose the ability to hear the higher ranges above 8,000 Hz

Amplitude Sound waves amplitude would cause a pressure on the ear drum human can detect amplitudes of less than one billionth of an atmosphere

At the top end of the audible range the pressure can cause pain a million times greater than the lower end but still one one-thousandths less than one atmosphere

Sound level is measured in decibels Because of the wide range in pressure variations, sound pressures and measured by a quantity called sound level Sound level is measured in decibels Barely audible – 10 dB Jet Engine 140 dB

Loudness is the human perception and depends upon both sound frequency and sound level

The Doppler Effect The change in pitch of a source because of the motion of either the source, the receiver, or both

If the source and receiver are moving closer together then the frequency would be higher frequency would be lower if they are moving apart

bats catch flying insects Applications of Doppler Effect radar detectors baseballs, cars, tennis balls astronomers determine speeds and distances of distant galaxies physicians ultrasound bats catch flying insects