2. Warm up The wavelength of water waves in a shallow dish is 7.5 cm. The water moves up and down at a rate of 5.6 oscillations per second. a.What is the speed of the wave? b.What is the period of the wave?

3. Physics Honors AB –Day 4/13 & 4/14/16 Sound

4. Agenda Properties of sound waves Humans and sound Doppler effect Standing waves

5. Sound

6. Sound is a wave Sound waves travel as a longitudinal, pressure wave Formed when an oscillating object creates alternating regions of compressed and expanded air Pitch = frequency Intensity = amplitude

7. Sound waves propagate…

8. Example Problem You drop a stone from rest into a well in which the water is 7.35 m below the top. How long does it take before you hear the splash?

9. Sound can also have frequencies we can’t hear… Humans can hear between 20 Hz and 20,000 Hz Infrasonic – sound with frequency below 20 Hz Ultrasonic – sound with frequency above 20,000 Hz

10. What happens a source that is moving? Doppler effect car horn Doppler effect – when a sound source moves towards or way from an observer, the apparent frequency heard by the observer at different frequencies

11. Doppler Effect

12. Example Problem A train is approaching a station. The train is traveling at 21.2 m/s and sounds it horn, which has a frequency of 655 Hz. What is the frequency of the horn to the observer as it approaches the station? What is the frequency of the horn to the train engineer?

13. What happens when an object travels so fast, it moves faster than the sound it produces Breaking the sound barrier

14. So how do human ears hear this sound

15. Human Hearing a | Scanning electron microscopy (SEM) image of three rows of outer hair cells that is viewed from the top of the organ of Corti and that shows unidirectional orientation of V/W-shaped hair bundles. b | Close-up view of one of these almost-mature hair bundles that consists of three rows of individual stereocilia and a true cilium, the kinocilium (white arrow), which is always positioned at the vertex of the bundle. Images in panels a and b were obtained from the middle cochlear turn of a wild-type mouse at postnatal day 7. c | Side view of a mature outer hair cell bundle that shows the precise staircase organization of stereocilia rows. d | Sound-induced, nanometer-scale deflections of the hair bundle 13 open mechanically gated ion channels (shown in red) 10, 11. These channels are thought to be located at the ends of tip-links 126. e | The tip-link 92 (indicated by white arrows) is a tiny filament that connects neighbouring stereocilia. Images in panels c and e were obtained from the middle cochlear turn of an adult guinea pig. 13 10, 11 126 92

16. Cochlear Implants

17. How do our ears perceive loudness

18. Example problem

19. Just for fun The Big Bang and Doppler effect