1. Sound Pitch Loudness Beats Doppler Effect
Physics
Ms. Shaver

2. Sound Sound is a longitudinal mechanical wave
aka a pressure or compression wave
Compressions(High Pressure)
Rarefactions(Low Pressure)

3. Sound
Tiny hairs inside the inner ear (cochlea) translate air pressure into electrical impulses that can be read by the brain

4. Graphing Sound

5. Speed of Sound Depends on the medium.
The more elastic the medium the faster sound will travel through it. 
Speed in metals>speed in water>speed in air
Sound can’t travel through vacuum.

6. Speed of Sound in Air v = 331 + 0.6 T ( in meters/sec)
T is the temperature in 0C.
In higher humidity, sound will travel faster.
For 15°C, v = *15 = 340 m/s
Use 340 m/s as an average speed of sound in air.

7. Faster than the speed of Sound
Supersonic – motion faster than speed of sound
Sonic boom – caused by an object breaking the sound barrier (supersonic planes, bullets)

8. Plane reaches speed above 770 mph – Explosion of sound waves caused by air crashing behind the plane
The air can condense or sweep up vapor from engine – causing this picture

9. Pitch: the frequency of a sound wave.
Musical notes have a given pitch.
The note C has a frequency of 327Hz.
When two notes differ by a ratio of 2:1 they are one octave apart.
What would be the next higher C? (Ans:654Hz)

10. Pitch – frequency of sound wave
Humans can hear frequencies between 20 Hz and 20,000 Hz
Infrasonic frequencies: Below 20 Hz
used by elephants and submarines to communicate over long distances
Ultrasonic frequencies
Dog whistles

11. Loudness = Amplitude Loudness is measured in decibels (dB)
A +10 dB change we hear as twice as loud
A -10 dB change we hear as half as loud

12. Decibels – Loudness measure
EXAMPLE: If a sound is 20 dB loud, answer how many dB these would be:
A sound twice as loud:
A sound half as loud:
A sound three times as loud:
30 dB
10 dB
35 dB

13. Decibels – Loudness measure

14. Examples of Sound Intensity Levels
jet plane taking off dB
air raid siren dB
threshold of pain dB
loud rock music dB
ear damage starts dB
busy traffic dB
normal conversation dB
quiet library dB
soft whisper dB
threshold of human hearing dB

15. Timbre – tone quality
What makes a particular musical sound different from another, even when they have the same pitch and loudness
EX: difference between a guitar and a piano playing the same note at the same loudness
Sounds can be described in terms of “coloration,” e.g. bright, dark, warm, harsh, etc.

16. Timbre – tone quality
Color of the note is due to the presence of different harmonics.
The “oo” has mostly low harmonics, while the “ee” has mostly high harmonics

17. Harmonics - Review
v = λ f - The velocity of the wave stays the same, even if considering different harmonics….it’s still the same wave!!!

18. Harmonics - Review

19. Properties of Sound Reflection (Echo) Refraction Interference
Diffraction

20. Echoes
Echoes are sounds that are reflected back by a hard boundary.

21. Echoes
Echolocation – used by many animals like bats to see through dark water or at night
Sonar – sound through water
Radar – light waves through air
Sonograms – sound waves through the human body

22. Beats Interference effect
When two waves of close frequencies interact causing alternating constructive and destructive interference

23. Beats
The number of beats = difference of two frequencies (absolute value)
EX: f1 = 345 Hz; f2 = 342 Hz
Number of beats = 345 – 342 = 3
There will be three beats per second
champions.com/science/sound_beat_frequencies.htm#.U2gpwletJW8

24. Bow (Shock) Waves
When the speed of a moving sound source is greater than the speed of the wave, a pressure ridge builds similar to the wave created by the bow of a ship.
physlet animation

25. Sonic Boom
When the pressure ridge of a bow wave of a jet passes over an observer on the ground, the observer experiences a sonic boom.

26. Doppler Effect
The change in a wave's perceived frequency due to the motion of either the sound source or the observer. 
It is applicable to any type of wave.
Austrian physicist Christian Doppler ( ).
train sound clip
Simulations
physlet animation

27. The Doppler Effect

28. The Doppler Effect
In front of the source the sound waves are compressed (shorter wavelength λ) and this raises the frequency (pitch)
Behind the source the sound waves are stretched (longer wavelength λ) and this drops the frequency (pitch)
Anything moving at the same speed as the source will experience no change in frequency