SoundSound Physics 102 Chapter Fourteen Amanda Hyer

20 Hz to 20,000 Hz infrasonic ultrasonic Compressions rarefactions Audible Frequency Range

Ultrasonic infrasonic 20 kHz 20 Hz Audible Frequency

Elastic Media Air Helium water rock steel slow fast speed=wavelength x frequency

Speed of Sound Speed = 331 m/s Tc speed = 343 m/s at 20 °C d=v x t ~ 1 km in 3 sec or 1 mile in 5 sec

Classical calculation of Sound Speed

Bulk Modulus for Air

ExerciseExercise How far away is a lightening bolt that is heard 12.0 sec after the flash is seen? Given: t=12.0 sec and v =1/3 km / sec Wanted: d Solution: Use d= v t d = (1 / 3 km/sec) (12.0 sec)= 4 km

ReflectionReflection

RefractionRefraction The bending of sound because the speed is different in adjacent regions

RefractionRefraction source far away

RefractionRefraction source far away warm cool Afternoon

RefractionRefraction source far away warm cool Late Evening

Energy in sound High frequencies dissipate faster than low. loud tuning fork versus soft tuning fork.

ResonanceResonance system that has a natural frequency like a tight string or a tube (flute) driven by a tiny oscillating force Resonce occurs when the frequency of the force matches the natural frequency of the system.

Interference When two waves overlap they form an interference pattern which can be either a constructive interference or a destructive interference. + = Constructive += Destructive Reinforcement Cancellation

InterferenceInterference Constructive (in Phase) Destructive (180 ° out of phase)

InterferenceInterference

BeatsBeats When two different frequencies merge beats are heard The Beat frequency is the difference between the two frequencies.

BeatsBeats

ExerciseExercise What is the beat frequency when a sound of 256 Hz meets a sound of 260 Hz Given: F1=256 Hz and F2= 260 Hz Wanted: F beats Solution: Use F Beats = Abs(F1 - F2) F Beats = Abs(F1 - F2) = 4 Hz

ResonanceResonance system that has a natural frequency like a tight string or a tube (flute) driven by a tiny oscillating force Resonce occurs when the frequency of the force matches the natural frequency of the system.

Standing Waves on a String

Open Organ pipe

Organ Pipe Closed at one end

Am and Fm broadcasting AM Amplitude Modulation carrier wave kHz FM Frequency Modulation M Hz

Am and Fm broadcasting Radio waves are electromagnetic waves Their speed is 300,000,000 m/s They travel through outer space Sound is an acoustical wave The speed of sound is 340 m/s They do not travel through outer space

Am and Fm broadcasting Radio waves are electromagnetic waves Their speed is 300,000,000 m/s They travel through outer space Sound is an acoustical wave The speed of sound is 340 m/s They do not travel through outer space

Carrier Frequency

AM broadcasting

Fm broadcasting