PH212 Lecture Notes - Lecture 6: Infrasound, Hertz, Waves
25 Dec 2018
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A vibrating object that creates alternating compressions and rarefactions. True or false: if object vibrating with shm, then air molecules vibrate back/forth with shm. No, there is no net displacement of air molecules. ~ 20 hz to 20 khz depends on age, # rock concerts. Elephants (14 24 hz), blue whales (10 - 39 hz), rhinos (down to 10 hz) List frequency type from lowest to highest: infrasonic : < 20 hz, audible range : 20 hz 20 khz. Pitch perceived highness/lowness of sound (what humans perceive as high or low. What happens when you go up an octave: you double the frequency, middle c = 264 hz, one octave higher c = 528 hz. Very, very high frequencies; ultrasonic waves are used (20, 000 hz +) because their wavelengths are extremely short. These waves are shorter and occur more often and thus detect smaller objects easily.
