1. What is sound? Sound is a longitudinal wave produced by a vibrating source Examples of sources: tuning fork, vocal cords, lips or reed on a musical instrument The vibration produces COMPRESSIONS and RAREFACTIONS in the air Must have a medium to travel through, will not travel through a vacuum http://dev.physicslab.org/Document.aspx?doctype=3&filename =WavesSound_IntroductionWaves.xml

3. Sound waves propagate in three dimensions Compressions and Rarefactions produce wave fronts that become a spherical wave Energy radiates outward from sound source in a direction perpendicular to the wave front.

4. What determines pitch? Pitch is the audible sound our ears perceive, and it depends upon FREQUENCY Higher frequency = higher pitch If sound source is moving, the perceived frequency of the hearer will change, so the pitch will change This is called the DOPPLER EFFECT

5. Doppler Effect Misconception the frequency does not change as the moving source approaches or recedes the frequency only changes as the moving source passes you ( the perceived frequency)

6. Resonance Resonance occurs when the frequency of a force applied to a system matches the natural frequency of the system Result: large amplitudes of vibration Example: breaking glass with your voice http://www.youtube.com/watch?v=ofESdVdX-fY

7. OR a bridge collapsing

9. Beats

12. The beat frequency (how often the beat is heard) is determined by the difference in the source frequencies Example: A tuning fork at 440 Hz and 448 Hz are struck at the same time. What is the beat frequency produced by the two sound waves? As the sound source frequencies are farther and farther apart…. Beat frequency is created by superposition/interference- there is constructive & destructive interference that creates the beat

13. What determines volume? Energy of a wave is determined by amplitude Volume of sound is also determined by amplitude How do we measure volume? On the Decibel (dB) scale Measure of sound intensity

14. rate at which energy flows through a unit area perpendicular to the direction of wave motion intensity = Δ E / ( Δ t area) = P / area Since the area of a sphere is equal to 4 π r 2, Intensity = P / 4 π r 2 (units: W/m 2 ) E: energy (J) t: time (s) P: power (W) r: radius from source (m) Intensity

15. Decibel (dB) describes the ratio of two intensities of sound; the threshold of hearing is commonly used as the reference intensity Ratio = Intensity of source/threshold of hearing threshold of hearing = 1.0 x 10 -12 W/m 2 logarithmic scale Means that an increase of 10 dB is power of ten increase (ten fold increase) in intensity

16. Intensity (W/m 2 ) Decibel level (dB) Examples 1.0 x 10 -12 0threshold of hearing 1.0 x 10 -10 20quiet whisper 1.0 x 10 -8 40mosquito buzzing 1.0 x 10 -6 60air conditioning at 6m 1.0 x 10 -4 80 busy traffic, alarm clock 1.0 x 10 -2 100subway, power motor 1.0 x 10 0 120threshold of pain 1.0 x 10 3 150nearby jet airplane

17. Human hearing

18. Audiogram