1. Chapter 15 Sound

2. 15.1 Properties of Sound Sound Waves
longitudinal wave
mechanical wave
has properties similar to water
reflection
refraction
diffraction
interference

3. 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

4. 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

5. 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

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

7. 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

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

9. 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

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

11. 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

12. 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

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

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

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

16. 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