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Characteristics of Sound

Characteristics of Sound. What Produces Sound? ?. If a tree falls in a forest and no one is there to hear it, will there be sound?. What produces sound?. Sound waves originate from a vibrating source Sound is also known as a “pressure wave”

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Characteristics of Sound

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  1. Characteristics of Sound

  2. What Produces Sound?? If a tree falls in a forest and no one is there to hear it, will there be sound?

  3. What produces sound? • Sound waves originate from a vibrating source • Sound is also known as a “pressure wave” • This is because vibrations cause changes in pressure near the source

  4. Vibrating Sources • http://www.youtube.com/watch?v=iYpDwhpILkQ • http://www.youtube.com/watch?v=3zoTKXXNQIU&feature=fvw

  5. To Do • Prove that sound is a pressure wave..... • In groups of three, light a candle and use the pressure generated by your voice to see if you can blow it out • Determine the characteristics of sound (frequency/amplitude) that are the most successful

  6. Characteristics of Sound • Sound travels in longitudinal waves • Has areas of high pressure (compressions), normal pressure, and low pressure (rarefactions)

  7. Bell Jar Experiment • http://www.youtube.com/watch?v=ce7AMJdq0Gw

  8. Characteristics of Sound • Bell jar experiment tells us that sound cannot travel through a vacuum. • Sound requires a medium....which type of wave is this? • Sound is capable of travelling through different types of solids, liquids, and gases. • In which medium would sound travel the fastest?

  9. To Do • Fill up one balloon with air and the other balloon with carbon dioxide (use baking soda + vinegar to produce carbon dioxide) • Investigate the differences in sound between the two mediums • Hold the balloon between your ear and some source of low-volume sound (i.e. Ticking watch). Compare the sound to the air filled balloon • Experiment with various sources of sound & record results

  10. Speed of Sound • At normal atmospheric pressure and 0 degrees C, the speed of sound is 332 m/s • If air pressure stays the same and temperature increases, speed of sound increases by 0.6 m/s per degree C. • Speed of sound in air = (332 + 0.6 T)m/s • ** T = temperature in degrees Celsius

  11. Practice Questions • What is the speed of sound at 20 degrees C? • What is the speed of sound at – 20 degrees C? • What is the speed of sound in air at 35 degrees C? • How much time is required for sound to travel 1.4 km through air if the temperature is 30 degrees C?

  12. Physics – Speed of Sound Answer Key 1) • V = (332 + 0.6 (20))m/s • V = 344 m/s 2) • V = (332 + 0.6 (-20)) m/s • V = 320 m/s 3) • V = (332 + 0.6 (35)) m/s • V = 353 m/s 4) • V = (332 + 0.6 (30))m/s • V = 350 m/s • 1400 m x 1second/350 m = 4s

  13. Frequency of Sound Avg. Human can respond to frequencies between 20 and 20 000 Hz. < 20 Hz are called infrasonic >20 000 Hz are called ultrasonic • Dogs  15 – 50 000 Cats  60 – 65 000 • Bat  1000 – 120 000 Moth  3000 – 150 000

  14. Frequency of Commonly Heard Sounds Male speaking voice – 120 Hz Female speaking voice – 250 Hz Highest piano note – 4186.01 Hz Stereo system – 15 – 30, 000 Hz Dog – 452 – 1080 Hz Cat – 780 – 1520 Hz Bat – 10 000 to 120 000 Hz Silent dog whistle – 20 000 to 24 000 Hz

  15. Frequency vs. Wavelength

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