1. Sound

2. Sound Waves Caused by vibrations Longitudinal or compressional waves
Mechanical waves - require a medium
Travel fastest in solids, then liquids, and slowest in gases

3. Characteristics Loudness --> Amplitude Pitch -->Frequency
Sound Intensity -->Energy

4. Range of Hearing in Humans
Average range is 20 – 20,000 Hz
Infrasonic - frequencies below 20 Hz or below the range of hearing for humans
Ultrasonic - frequencies above 20,000 Hz or above range of hearing for humans

5. Speed of Sound in Air
The speed of sound in air changes with temperature.
The speed at 0° C is 331m/s for dry air
It increases by 0.6 m/s for each degree Celsius above zero.

6. Speed of Sound con’t
at three times the speed of sound

7. Echoes
An echo is a reflected sound wave
An echo travels to a barrier and then reflects back

8. Echo Problems
 es

9. Beats
Beats occur due to interference patterns between sound waves of slightly different frequencies. Hear alternating loud and soft sounds.
Humans can only hear beat frequencies of
7 Hz or less.
Δf = beat frequency, beats/sec or Hz
f1= frequency of one sound, Hz f2 = frequency of another sound, Hz

10. Resonance
A condition that exists when the frequency of a force applied to an object matches the natural frequency of vibration of the object.
The object will then begin to vibrate with sympathetic vibrations.
An extreme example of resonance is the collapse of the Tacoma Narrows Bridge.

11. The Doppler Effect
A frequency shift that is the result of relative motion between the observer and the source of sound.
The Doppler effect occurs with any type of wave.
For sound, if the source of sound is approaching an observer, a higher pitch (or frequency) will be heard.
If the sound is going away from an observer, a lower pitch (or frequency) will be heard.

12. Doppler Effect f ' = apparent frequency (detected freq), Hz
f = frequency of source (emitted freq), Hz
v = velocity of sound in air, m/s
vo = velocity of observer or detector, m/s
vs = velocity of source of sound, m/s
Note: Use if v is not given.

13. Doppler - continued
Use if the observer and source are getting closer together (hear higher pitch)
Use if the observer and source are getting farther apart (hear lower pitch)

14. General Wave Formulas

15. Sound Formulas

16. Remember units! Frequency -- Hertz (cycles/sec) Period -- seconds
Wavelength -- meters
Wave speed -- m/s
Sound Intensity -- W/m2
Relative sound intensity -- decibels (dB)