2. Reflection of Sound Ms.Rhodes Physics CP1

3. What happens when a sound wave changes medium or encounters an obstacle?

4. 1. Reflection off obstacle. Bounces back 2. Transmission- travels into new medium (gets absorbed) 3. Diffraction around obstacle

5. Diffraction 1.Depends on size of obstacle compared to wavelength. 2. Larger wavelengths diffract more than smaller ones.

6. Diffraction Lower frequency = longer wavelengths!

7. Diffraction Travel great distance!Reflect Back!

8. "The angle of incidence is equal to the angle of reflection" reflection LAW OF REFLECTION

10. 2. Shape of obstacles 1. Dissimilarities of Medium Reflection depends on…

11. Reflection #1 Dissimilarity of Mediums More dissimilar = more reflected Air –concrete = More reflected, less transmitted (absorbed) Air – foam = less reflected, more transmitted (absorbed)

12. REFLECTION #2 Shape of obstacle Parabolic shape focuses sound to one focal point

13. http://www.nde-ed.org/EducationResources/HighSchool/Sound/reflection.htm

14. Reflections / shape Satellite Discs Bull Moose Owl – Facial Discs Parabolic Microphones (megaphones) Hollywood Bowl

15. In Auditoriums, do you think they use smooth or rough walls? Why?

17. Rough Walls = reflect sound in a variety of directions LIVELY FULL SOUND Smooth Walls = reflect sound in specific direction LESS LIVELY AND FULL

18. http://www.nde-ed.org/EducationResources/HighSchool/Sound/reflection.htm

19. REFLECTION REFLECTION LEADS TO TWO PHENOMENONS »ECHO »REVERBERATIONS

20. Reverberation Reflection that occurs in a room less than 17 meters wide Brain stores sounds for 0.10 th of a second Sound reflected back will reach you in less than 0.10 th of a second Sound seems prolonged to person http://www.youtube.com/watch?v=cYMQme4quOE

21. Reverberations Examples talking in an empty room honking horn in a tunnel singing in the shower

22. Reverberation Times Orchestras = 1-2 sec reverb time Choral music = 2-5 sec reverb time No reverb time = anechoic

23. ECHOES Reflection that occurs in an area greater than 17 meters wide Sound reflected back will reach you later than 0.10 th of a second Sound sounds like a separate and distinct sound from the original

24. SONAR SOund Navigation And Ranging Measures time to travel to bottom and return When depth gets deeper, the time to travel for the sound increases. Time variation displayed on display

25. Bats Echolocation

26. RADAR Radio Detection and Ranging Sends out high frequency radio pulses, reflected back as echoes Radio waves travel at speed of light Time of reflection depends on objects distance away. Time Variation displayed on screen.

28. You can determine distance, time and speed of sound from echo.

29. You can determine distance, time and speed of sound from echo. #1. Time how long it takes to hear echo.

30. Look up temp on your phone… Speed of Sound= 332 + 0.6(Temp)

31. Speed= distance / time Solve for distance NOTE: distance to cliff = 1/2distance

32. Sample Problem Indiana Jones yells across the cliff to Shorty who is on the other side and hears his echo 4.0 sec later. It is a warm day of 37 Celsius. How far away is Shorty?

33. Known Variables Time = 4 seconds Temp = 37 C V = 332 + (0.6T) V = 332 + (0.6 * 37) v = 354.2 m/s Speed = distance/ Time 354.2 = distance/ 4 1416.8 = distance distance to other side = ½ d distance to other side = 708.4 m Solve for Speed of Sound Solve for distance

34. Homework: 1.Sound Reflection Math 2.Sound Reflection Concept