1. Barry Latham Physics: Principles & Problems Glencoe Science, 2005

2. 15.1: Properties and Detection of Sound Sound Waves- pressure variation transmitted through matter Speed of Sound- =v/f PhET “Wave Interference”

3. Detection of Pressure Waves Human Ear Tympanic membrane vibrates at the same frequency as the pressure variation Three tiny bones transfer motion to cochlea Tiny hairs in cochlea are sensitive to vibration Nerve cells send impulses to the brain Ear Animation.swf

4. Perceiving Sound Pitch- human perception of frequency Approximately 20Hz-16,000Hz is the audible range Loudness-human perception of amplitude Sound level- logarithmic scale of pressure variations Decibel (dB)- unit of loudness 10x higher pressure represents an increase in 20dB Humans perceive an increase of 10dB as being twice as loud

5. The Doppler Effect Doppler Shift- change in frequency due to motion between the sound source and receiver Physics Physlet I.18.4 (Doppler Effect.swf) Motion only depends on the objects getting closer or further away. It doesn’t matter who does which. Blue Shift- objects getting closer Source stationary, receiver moving towards source Receiver stationary, source moving towards receiver Red Shift- objects getting further apart Source stationary, receiver moving away from source Receiver stationary, source moving away from receiver

6. Doppler Effect f d =f s (v-v d )/(v-v s ) f s =frequency of source(Hz) f d =detector (your ear?) v=velocity of sound (m/s) v s =velocity of source (m/s) v d =velocity of detector (m/s) Takes into account direction, so be cautious with positive and negative signs Super Mario Sound Barrier.swf

7. 15.2 The Physics of Music Sources of Sound Air rushing from lungs through vocal cords Lips vibrating in the mouthpiece of a brass instrument A wooden reed vibrating in a clarinet (woodwind) Strings vibrating in a guitar, piano, harp, etc.

8. Resonance in an Air Column Closed-pipe resonator- tuning fork above a hollow tube The tube can be adjusted so that it resonates with the tuning forks frequency Loudest at the resonance point(s)- amplitudes are added together

9. Standing Pressure Wave Open-pipe resonator- similar to closed-pipe, but not sealed at the other end Sound wave reflects off of open end and is inverted

10. Closed vs Open Pipe Resonators

11. Resonance Frequencies Closed-pipe resonators- the shortest pipe length that will resonate is /4=L 1 All additional resonances occur with the addition of /2 to the pipe length /4=L 1, 3 /4=L 2, 5 /4=L 3, 7 /4=L 4, etc. Open-pipe resonators- the shortest pipe length that will resonate is /2=L 1 All additional resonances occur with the addition of /2 to the pipe length /2=L 1, =L 2, 3 /2=L 3, 2 =L 4, etc. Resonance tubes.swf

12. Resonant Frequencies Closed Pipe Open Pipe Resonance Tubes.swf

13. Resonance on Strings Strings act as open-pipe resonators First resonance is at =L 1, though, not /2 =L 1, 3 /2=L 2, 2 =L 3, etc.

14. Closed-Pipe Harmonics For 1 in a closed-pipe instrument, that frequency is the fundamental frequency, f 1 Each additional odd-numbered resonance point is the next harmonic 3  f 3, third harmonic 5  f 5, fifth harmonic 7  f 7, seventh harmonic

15. Open-Pipe Harmonics For 1 in an open-pipe or stringed instrument, that frequency is the fundamental frequency, f 1 Each additional resonance point is the next harmonic 2  f 2, second harmonic 3  f 3, third harmonic 4  f 4, fourth harmonic

16. Consonance, Dissonance & Beats Dissonance- an unpleasant set of pitches played at the same time Consonance- a pleasant set of pitches played at the same time (a chord) Both experiences are culturally influenced Physics Physlets E.18.1, E.18.2 Beats- oscillation of amplitude due to two frequencies being slightly different f beat =|f A -f B | Used to tune instruments- when the beats slow down and disappear, the instrument is in tune