Text of Chapter 16 – Waves and Sound. 16.1 – The Nature of Waves A wave is a traveling disturbance that...
Chapter 16 Waves and Sound
16.1 The Nature of Waves A wave is a traveling disturbance that carries energy. Transverse Wave disturbance is to wave direction (up and down); light, vibrating strings. Longitudinal Wave disturbance is // to wave direction (compression); sound.
16.2 Periodic Waves time required for 1 cycle (sec) number of waves per unit time (Hertz or Hz) length of the wave (m) max. displacement during a cycle (m) Period (T) - Frequency (f) - Wavelength () - Amplitude (A)
The speed of a wave (v) is determined by dividing the wavelength by its period. Remember that
16.3 SKIP 16.4 SKIP 16.5 The Nature of Sound Sound L-wave created by a vibrating object; needs a medium (solid, liquid, gas) for the disturbance to travel.
Sound is NOT a mass movement of air, the air molecules are in SHM
16.6 SKIP 16.7 Sound Intensity Sound waves carry energy that can do work. POWER = Energy/Time [Joule/sec] = [Watt] Sound Intensity (I) Power/Area [Watt/m 2 ] Threshold of hearing = 10 -12 W/m 2
16.8 Decibels (dB) The ear responds to sound in a logarithmic way. Intensity Level () compares sound intensity to a reference level; logarithmic ratio.
A 1-dB change in intensity level is smallest change noticeable by humans. When intensity level increases by 10 dB, the new sound seems ~ 2X louder. Ex. 70 dB is twice as loud as 60 dB. REVIEW of TERMS Power [Watt], Intensity [Watt/m2] Intensity Level [dB], Loudness - subjective
Table of sound levels L and corresponding sound pressure and sound intensity Examples Sound Pressure Level L p dBSPL Sound Pressure p N/m 2 = Pa Sound Intensity I W/m 2 Jet aircraft, 50 m away140200100 Threshold of pain13063.210 Threshold of discomfort120201 Chainsaw, 1m distance1106.30.1 Disco, 1 m from speaker10020.01 Diesel truck, 10 m away 900.630.001 Curbside of busy road, 5 m 800.20.0001 Vacuum cleaner, distance 1 m 700.0630.00001 Conversational speech, 1m 600.020.000001 Average home 500.00630.0000001 Quiet library 400.0020.00000001 Quiet bedroom at night 300.000630.000000001 Background in TV studio 200.00020.0000000001 Rustling leaf 100.0000630.00000000001 Threshold of hearing 00.000020.000000000001
ASSIGN: Chapter 16 # 8, 51, 63, 66; Page 489 Due Do your homework, kid
16.9 The Doppler Effect The observed frequency (pitch) of a sound increases as the sound comes closer; lowers as sound moves away.
16.9 The Doppler Effect
16.10 SKIP 16.12 SKIP
The ear can respond to sounds within the 20 to 20 kHz range. The ear is most sensitive to sounds b/w 1-5 kHz Most alarms (and screams) are near the 1-5 kHz range. Did human speech evolve to match the frequency band the ear is most sensitive to OR did the ear evolve to be sensitive to the frequency band humans mostly speak at OR is it all just a coincidence??? 16.11 The Sensitivity of the Human Ear
dBA weighted dB scale that approximates human sensitivity to different frequencies.