1. Sound

2. Characteristics Loudness --> Amplitude Pitch -->frequency

3. Wave Formulas

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 –Used for ultrasound equipment (like ‘seeing’ a baby in utero)

5. Sound Waves Longitudinal or compressional waves Require a medium Travel fastest in solids, then liquids, and slowest in gases

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

7. Echoes An echo is a reflected sound wave An echo travels to a barrier and then reflects back Note: So time is usually given there and back but distance is given only one way (so either ½ the time or double the distance).

8. Doppler Effect The resulting change in frequency of a wave due to changing distance between the wave source and the observer. As an object is moving while making periodic waves, the waves get closer together in front the object and spaced out behind it. –Closer waves = higher frequency = higher pitch –Spaced out = lower frequency = lower pitch Consider the sound of a passing train horn

9. Sound Intensity Measured in decibels (dB) A result of amplitude which depends on: – The amount of power used (watts) at the source –The distance between source and observer –More amplitude = louder –Less amplitude = quieter As a wave travels through a medium, it has to move each molecule, draining power. Eventually there is no power left. This is why sounds die out. –Imagine what you would experience if every sound wave went on indefinitely…

10. Concepts (log scale) A 10 dB increase = 10 times the pressureA 10 dB increase = 10 times the pressure A 10 dB increase = twice the loudnessA 10 dB increase = twice the loudness –This is why loud sounds can injure eardrums – loud sound = LOTS of pressure

11. Remember units! Frequency -- Hertz (cycles/sec) Period -- seconds Wavelength -- meters Wave speed -- m/s Sound Intensity -- W/m 2 Relative sound intensity -- decibels (dB)

12. Harmonics and Overtones Closed end – both ends are fixed with a node at each end (regardless of how many nodes in between). Ex) guitar string or xylophone Open end – one end is closed with a node at the fixed end, other end is open with an antinode at the loose end. Ex) flute or organ pipe

13. Harmonics and Overtones – closed end 1 st harmonic = 2 nodes = ½ wave = fundamental frequency 2 nd harmonic = 3 nodes = 1 wave = 1 st overtone 3 rd harmonic = ……2 nd overtone 4 th harmonic = …..3 rd overtone and so on...

14. Harmonics and Overtones – open end 1 st harmonic = 1 nodes & 1 antinode = ¼ wave = fundamental frequency 2 nd harmonic = 2 nodes & 2 antinode = ¾ wave = 1 st overtone… use length of pipe to calculate wavelength or vice versa use speed of sound = 343 m/s, if not given

15. 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.