CP Physics Ms. Morrison

 Mechanical – needs medium  Longitudinal  Created by vibrations which disturb the medium and transmit the wave energy  Sound pulses create compressions and rarefactions  Compressions – high pressure, particles pressed together  Rarefactions – low pressure, particles expand out

 Frequency = number of pressure oscillations per second (Hz)  Pitch = our impression of frequency  High pitch = high frequency and vice versa  Human range of hearing: 20 – 20,000 Hz ▪ Infrasonic = below 20 Hz ▪ Audible sound = 20 – 20,000 Hz ▪ Ultrasonic = above 20,000 Hz

 Loudness = our impression of sound intensity which is a measure of the wave’s energy (amplitude), measured in decibels (dB)  Barely heard = 0 dB  Sound 10x louder = 10 dB  Sound 100x louder = 20 dB

 Sound waves have all the same properties as other waves  Refract  Reflect  Diffract  Interference  Reflection of sound = echo

 331 m/s at 0 o C (32 o F)  343 m/s at 20 o C (68 o F)  Equation:v = λf  As temperature of air increases, so does the speed of sound  V sound = 331 m/s + 0.6(ΔT)  ΔT = change in temperature from 0 o C  Travels fastest through solids, then liquids, and slowest through gases  Travels fastest when medium is elastic and molecules close together

 Pitch higher when sound is approaching  Pitch lower when sound is moving away  Equation:f’ = f [(v + v d )/(v – v s )]  f’ = perceived frequency  f = actual sound frequency  v = speed of sound (assume 343 m/s, unless otherwise specified)  v d = velocity of detector (+ towards source, - away from source  v s = velocity of source (+towards detector, - away from dectector)

 Human voice (singing) = vocal cords  Brass instruments (tuba, trumpet) = musician’s lips  Reed instruments (clarinet, saxophone) = reed  String instruments (piano, guitar, violin) = string against sounding board  Other instruments (flute, recorder) = air moving inside column

 Forced vibration = vibration of an object causes another object or material to vibrate  Natural frequency = frequency at which a minimum amount of energy is needed to make object vibrate (need least amount of energy to continue vibrations

 Resonance = forced vibration of object that matches its natural frequency  Results in a dramatic increase in the wave’s amplitude – sounds louder  Examples: swinging on swing, bridge vibrations, opera singer breaking glass  Can cause damage – Tacoma Narrows Bridge (1940)  Soldiers “break step” when crossing bridges to prevent resonance

 Interference of sound waves (often occurs during resonance)  Constructive – waves are in phase, sound gets louder  Destructive – waves are out of phase, sound gets softer or no sound at all

 Beats = difference in frequencies between two sounds heard simultaneously  Used to tune instruments – when frequencies are equal, then beat disappears  Find beat frequency by taking difference between two frequencies

 Sonar – uses echoes to determine the distance of objects  Bats – use echo location to determine distances of objects as they fly  Ultrasound – use sound waves to “see” inside humans and other materials  Relies on Doppler shift  See unborn babies  Examine heart (echocardiogram) and other organs