1. What is sound? define, define, define! Changes in air pressure Perception of the changes We can hear from about 15 changes per second to 20000 changes per second (Hz)

2. “If a tree falls in a forest far from any sound detector (human ear, microphone, etc.), does the tree's fall make any noise?”

3. Know thy “enemy”

4. Did you know? Changes in air pressure perceived as sound are the same as…

5. Did you know? Changes in air pressure perceived as sound are the same as… …changes in air pressure discussed in meteorology

6. Did you know? Changes in air pressure perceived as sound are the same as… …changes in air pressure discussed in meteorology Difference? Weather – greater magnitude, and change far more slowly

7. So many waves, but which is the one… Nice animated examples: http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/waves/u10l1c.html

8. Sound - longitudinal

9. Sound vibrations, vibrations, vibrations

10. Sound simple harmonic motion

11. Simple harmonic motion Vibrating system Common property: motion repetitive

12. 1.Period – time between two repetitions (duration of one cycle) 2.Wavelength – the distance between corresponding points, from cycle to cycle as the wave repeats itself 3. Frequency – how often the wave repeats itself during time unit 4. Amplitude – how high and low wave oscillations are 5. Phase – position of a wave at a certain time Simple harmonic motion

13. Refraction wave bends(refracts) around the object Obstacle size: smaller than a wavelength

14. Reflection the wave reflects away from the object Obstacle dimensions significantly larger than wavelength any change in the medium

15. Reflection on a string

16. Reflection within a tube

17. Superposition waves in a crowd

18. Standing waves

19. STRING bound at both ends

20. Tube closed at both ends

21. Tube opened at both ends

22. Tube closed at one ends

23. Velocity and pressure