1. More On Sound

2. Quality How you can tell one sound source from another even when playing the same frequency Depends on the presence of overtones

3. Tuning Fork Guitar

4. Noise Unpleasant combo of overtones

5. Sound Interference When sound waves travel through the same space, they interfere with one another In some places they interfere constructively and the sound intensity is amplified In some places they interfere destructively and intensity is decreased Constructive interference occurs every whole wavelength while destructive interference occurs every ½ wavelength

6. Beat When two sounds are close in frequency they can interfere with one another over time You will hear alternating loud and and soft sounds

8. Beat Frequency Number of loud sounds heard per second B =  f 2 – f 1  Human ear can only detect beat frequencies less than 7 Hz (difference in frequency of 7 Hz) Used to tune instuments

9. Example A tuning fork produces a steady 400Hz tone. When struck and held near a guitar string twenty beats are counted in 5 seconds. What are the possible frequencies of the guitar string?

10. Mach Supersonic Speed – faster than sound Mach – ratio of speed of an object to the speed of sound Mach = speed/ speed of sound

11. Example What is the speed of a plane traveling at Mach 3?

12. Sonic Boom When an object approaches the speed of sound, circular wave fronts pile up in front At point of pile up, air pressure is high – called the Sound Barrier (lots of turbulance) Once past the sound barrier, wave fronts pile up along the side Constructive interference creates high pressure area which sweeps the ground – Sonic Boom

15. Doppler Effect

16. What Is It? Pitch of an object appears to change as it passes a stationary observer In front of moving object, waves pile up creating area of higher frequency Behind waves spread out, lower frequency