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SOUND

SOUND. 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

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SOUND

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  1. SOUND SOUND Tiffany Rhodes Physics

  2. Topics Covered • Source • Wave • Medium • Frequency • Amplitude • Speed • Mach Number

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

  4. 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

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

  6. 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

  7. Can sound travel through space? Why?

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

  9. 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

  10. Range of frequencies

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

  12. Range of frequencies

  13. 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 http://www.youtube.com/watch?v=ydxoTPwFwjs

  14. 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 http://www.youtube.com/watch?v=RyIphO4Ypoo http://www.youtube.com/watch?v=oPWucNgN8TQ

  15. 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

  16. Speed of sound in Various Mediums • Carbon Dioxide 258 • Air 332 • Cork 500 • Alcohol 1241 • Fresh water 1500 • Marble 3810 • Steel 5050 • Aluminum 5104 • Earth 7000-13000

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

  18. SPEED EQUATION V = (332 + 0.6T) m/s V = Speed of sound T = Temperature in Celsius

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

  20. At 30 Celsius:V= (332 + 0.6 * 30)V = 350 m/s At –30 Celsius:V = (332 + 0.6 * -30)V = 314 m/s Hotter = Faster Cooler = Slower

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

  22. 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!

  23. 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

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

  25. Questions • Mach Number problems? • Wave Equation problems?

  26. A rocket is traveling at 8643.6 km/hr. If the air temperature is 20ºC, what is the rocket’s Mach Number? Warm Up

  27. Answer • Speed of object = 8643.6 km/h • Speed of sound = 332 + 0.6* Temp = 332 + 0.6 (20) = 344 m/s Convert to km/h 344m 1 km 3600sec 1 sec 1000m 1h = 1238.4 km/h Mach # = Speed of Object/Speed of sound = 8643.6/ 1238.4 = 7

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