SOUND Tiffany Rhodes Physics. Topics Covered Source Wave Medium Frequency Amplitude Speed Mach Number.

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Presentation transcript:

SOUND Tiffany Rhodes Physics

Topics Covered Source Wave Medium Frequency Amplitude Speed Mach Number

If a tree falls in the forest and nobody is around to hear it, does it make a sound?

I. EVERY SOUND IS CREATED BY A VIBRATION Guitar string vibrates Reed of clarinet vibrates Vocal cords vibrate Table top vibrates when hit with a hammer Brain translates vibration into sound

II. SOUND IS A LONGITUDINAL WAVE Compressions and rarefactions AIR DENSITY CHANGES AS SOUND ENERGY TRAVELS THROUGH Only energy is transported!!!!

III. SOUND NEEDS A MEDIUM Sound can travel through air, liquids, and solids Sound travels faster thru solids! Sound can NOT travel thru a vacuum

Can sound travel through space? Why?

IV. Frequency of Sound = PITCH LOW PITCH = LOW FREQUENCY HIGH PITCH = HIGH FREQUENCY 1 Hertz = 1 vibration/second

V. HUMAN HEARING Range 20 – 20,000hz Most sensitive at 200 to 4,000 Hz. Normal voice range is about 500 Hz to 2000 hz Low frequencies are vowels and bass. High frequencies are consonants Lose hearing as we age, especially at the high frequency end. Girls usually hear higher frequencies better than boys

Range of frequencies

FREQUENCIES Below 20 HZ = INFRASONIC Above 20,000 HZ = ULTRASONIC We can NOT hear either spectrum

Range of frequencies

VI. INTENSITY DEPENDS ON AMPLITUDE Intensity can be measured by an oscilloscope More Intense = Bigger amplitude Less intense = smaller amplitude Loudness is perceived intensity. Subjective om/watch?v=ydxoTP wFwjs

Intensity Unit of Intensity = Decibels (dB) Named after Alexander Graham Bell Zero Decibels = threshold of hearing Increase to 10 decibels (intensity increased by a factor of 10) Thus it is 10 times more intense 60 dB is 100 times more intense than 40 dB

Source of SoundLevel in Decibels Hearing threshold0 Normal Breathing10 Close Whisper20 Library40 Normal Speech60 Busy Street Traffic70 Average Factory90 Old Subway train100 Loud rock Music115 Threshold of Pain120 Jet Engine at 30 m140

VI. SPEED OF SOUND Medium Affects Speed 2 Properties of a medium affect speed –1. Elastic properties –2. Inertial property Temperature of medium also affects it. –Generally, Hotter = faster Cooler = slower –See Hand out for more information

Speed of sound in Various Mediums Carbon Dioxide 258 Air332 Cork500 Alcohol1241 Fresh water1500 Marble3810 Steel5050 Aluminum5104 Earth

Which medium would sound travel fastest through? Air Aluminum Ocean water Helium

SPEED EQUATION

What is the Speed of Sound in air at 30 C and –30 C?

At 30 Celsius: V= ( * 30) V = 350 m/s At –30 Celsius: V = ( * -30) V = 314 m/s

Mach Number What do you already know about Mach Number? Related to air planes?? Related to sound??

Mach Number Relates speed of object with speed of sound Usually used with aircrafts since they are our fastest means of travel Mach Number = Speed of Object/ Speed of sound Speed of object and sound have to have same units. They cancel out… Mach Number has No units!

What do you know about an airplane that travels at mach 1? It is traveling at the same speed of sound What do you know about an airplane that travels at mach 2? It is traveling double the speed of sound

II. Wave Equation Sound is a wave so therefore the wave equation still applies. Speed of the wave = wavelength * frequency V = * f

Questions Mach Number problems? Wave Equation problems?

Warm Up A rocket is traveling at km/hr. If the air temperature is 20ºC, what is the rocket’s Mach Number?

Answer Speed of object = km/h Speed of sound = * Temp = (20) = 344 m/s Convert to km/h 344m1 km 3600sec 1 sec1000m 1h = km/h Mach # = Speed of Object/Speed of sound = / = 7