1. Sound
Chapter 12

2. Sound Waves A pressure variation that is transmitted through matter
Sound waves move through air because a vibrating source produces regular oscillations in air pressure
Sound is a longitudinal wave

3. Temperature
The speed of a sound wave in air depends on the temperature of the air
Sound waves move through air at sea level at 343 m/s at room temperature (20° C)
Sound can also travel through liquids and solids at greater speeds than gases
Sound can not travel through a vacuum because there are no particles to move and collide

4. Other properties of waves
Reflect off hard objects
Echoes
Time for echo to return to source can be used to find the distance between the source and the object (sonar) v = λƒ
Can be diffracted
Can have interference with dead spots

5. Loudness Physical characteristics of sound waves
Frequency, wavelength, amplitude
Amplitude is the measure of the variation in pressure along the wave
Loudness
The human ear can detect a wide range of amplitudes, so they are measured on a logarithmic scale
sound level measured in decibels

6. Pitch Frequency of vibration is pitch
Each music note has a different frequency
Most people are sensitive to sounds with frequencies between 1000 Hz and 5000 Hz

7. Intensity Intensity is the rate at which energy is transferred
I = power / (4pi)(distance)^2
I = P / 4πr2
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8. Doppler Shift (Radar)
As a vehicle with a siren moves toward you the pitch changes
Frequency is higher when moving toward you and drops to a lower pitch as the source moves away
The frequency of the source does not change, but as the vehicle travels toward the listener more waves are compressed in the area
More crests reach the ear per second so the frequency of the detected sound increases

9. Physics of Music Sound (music) is produced by vibrating objects
Reeds, surfaces, cone, vocal cords, lips, pipe openings, air columns, strings, wires

10. Resonance in Air Columns
Resonance increases the amplitude of a vibration by repeatedly applying a small external force at the same natural frequency
The length of the air column determines the frequencies of the vibrating air
Changing the length of the column of vibrating air varies the pitch of the instrument

11. Resonating tube A hollow tube is placed in water to close one end
Closed-pipe resonator
A resonating tube with one closed end
The length of the air column is changed by adjusting the height of the tube above the water

12. Lab
The sound is loud when the air column is in resonance with the tuning fork
A resonating air column intensifies the sound of the tuning fork
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13. Open-pipe resonator
A resonating tube with both ends open that will resonate with a sound source is an open-pipe resonator
The sound wave does not reflect off a closed end but rather off an open end
The pressure of the reflected wave is inverted

14. Resonance lengths
A standing sound wave in a pipe can be represented by a sine wave
The standing waves have nodes and antinodes
Nodes are regions of low displacement
Antinodes are regions of high displacement
2 nodes or 2 antinodes are separated by ½ wavelength

15. Resonance Frequencies
Closed pipe
λ/4, 3λ/4, 5λ/4, 7λ/4, and so on will all be in resonance with a tuning fork
Open pipe
λ/2, λ, 3λ/2, 2λ, and so on will be in resonance with a tuning fork
P. 427 (1-3)

16. Beat notes
Two frequencies that are nearly identical interfere to produce high and low sound levels
This oscillation of wave amplitude is a beat
When the difference is less than 7 Hz, the ear detects a pulsation of loudness