Sound Notes Chatfield Senior High Department of Physics

Sound is a Wave  It is a longitudinal (1-D) wave

Properties of Sound  Transmission-sound goes through a material Reflection- waves bounce off at the same angle it was received Absorption- waves are blocked by a substance (opposite of transmission)

Transmission in space? Sound requires a medium to travel

Speed of Sound  It is variable based upon temperature and density of the material  Approximate values of speed of sound  Air (0 0-) 330 m/s  Air (25 o) 343 m/s  Water-1440 m/s  Glass-4550 m/s  Iron and Steel- 5000m/s

Lab 1- Verifying frequency of a tuning fork  Determine period of wave by averaging 10 wavefronts as below and then use f=1/T to verify frequency

FFT Curve

Lab 2-Sound through echo  Find distance of the tube and double it (why?)  Use v=d/t to determine the speed of sound in air.

Lab 3-Finding Resonance of Tube  Find frequency where sound rings out  The sound is reflecting off the water and therefore creates a closed ended tube  The  is basically a quarter of a wavelength (why?)

Resonance in Sound  Wavelengths that have the same amplitude and frequency that result in an increase of amplitude

Closed Ended Tube (Pipe organ)

Open-Ended Tubes and Strings (Organ / Guitar String) (1/2 

The decibel  A logarithmic scale that shows the loudness of sound L=10 A A= log L  Table of values Threshold of hearing- 0 dB Whisper-20 dB Library-40 dB Refrigerator-45 dB Restaurant- 50 dB Ordinary Conversation-65 dB Busy Traffic- 70 dB Screaming Child- 90 dB iPod at Maximum Volume-108 dB CSH Fire Alarm-115 dB Threshold of Pain-120 dB Jet Airplane-140 dB

Frequencies of Sound  The human ear hears sound from the range from Hz  We hear sounds the best from Hz

Frequencies of Music

Range of Audibility of the Human Ear

Ultrasound (Frequencies above human hearing)

Beats  Two waves constructively interfering whose frequencies are above or below each other

The Ear

Function of the Ear’s parts  Outer ear-pinna-collects sound  Middle ear-transmits vibrations to the inner ear  Inner ear-fluid transmitted to hair cells that have nerve endings (also used for balance)

Doppler Effect  When an object is moving toward the observer the pitch is higher  When an object is moving away from the observer the pitch is lower

Sonic Boom

Sound and Music  Most pure…the Blue Man Group