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SOUND

SOUND. Mrs. Gibson Chapter 16 Physical Science. Let’s Explore SOUND briefly. From The Soundry : http://library.thinkquest.org/19537/. Begin with a test; hold your middle and index finger over the middle of your throat. Say the word “Aah” softly, say it louder now. What do you observe?.

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SOUND

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  1. SOUND Mrs. Gibson Chapter 16 Physical Science

  2. Let’s Explore SOUND briefly From The Soundry : http://library.thinkquest.org/19537/ • Begin with a test; hold your middle and index finger over the middle of your throat. • Say the word “Aah” softly, say it louder now. • What do you observe? Sound is produced by the mechanical energy of vibrations. Sound waves are COMPRESSIONAL WAVES See Slinky Demo

  3. Compression Rarefaction Animation

  4. Remember - Waves • Four Parts to a Wave • Wavelength – horizontal length of one cycle of the wave. • Period – amount of time it takes a wave to travel one wavelength past a certain point.

  5. Four Wave Parts Continued • Amplitude – the height of the wave. • A large amplitude is a louder sound • A small amplitude is a quieter sound • Decibel measures sound intensity or amplitude

  6. Frequency Each sound wave has a condensation (compression) region and a rarefaction region behind it. Frequency is the number of condensations that pass a point in a second. Measured in Hertz Pitch – how the brain interprets frequency Higher the frequency, the higher the pitch Lower the frequency, the lower the pitch Example – if 900 condensations are generated every second then the Frequency is 900 Hz Four Wave Parts Continued

  7. Common Frequencies • Lower Hz mean lower pitch, such as Thunder at 500Hz • Higher Hz means higher pitch, such as a sopranos high note at 1000 Hz • Normal human ear can hear between 20 to 20,000 Hz (vibrations per sec) • Sounds higher than 20,000 Hz are called ultrasonic. • Sounds lower than 20 Hz are called infrasonic.

  8. Doppler Effect Pitch of a sound changes as it moves toward a receiver and then past the receiver. http://www.allthingsscience.com/video/326/The-Doppler-Effect See diagram on the next page.

  9. Diagram of Doppler Effect http://www.crocodile-clips.com/absorb/AP5/sample/040103.htmlhttp://www.colorado.edu/physics/2000/applets/doppler2.html From: http://www.glenbrook.k12.il.us/gbssci/phys/CLass/sound/u11l3b.html

  10. Explanation The sound of a siren as it approaches is higher because the sound waves are being pushed together, shortening the wavelength and increasing the frequency. As the siren passes the sound waves can spread out lengthening the wavelength and decreasing the frequency, thus lower pitch.

  11. Doppler Effect • Some bats, known as Doppler bats, are capable of detecting the speed and direction of any moving object by monitoring the changes in frequency of the reflected pulses.

  12. Speed of Sound Observe the Chart. Determine where sound travels fastest. Why? Does Temperature have an effect on the speed of sound?

  13. Speed of Sound • Remember Speed can be calculated using Distance/Time. • Using the speed of sound through 20 degrees Celsius air which is 343 m/s, what is the distance of an approaching storm in which the lightning appeared and 5 seconds later the thunder struck. • Use dimensional analysis to convert meters to miles.

  14. Speed of Sound • MACH speed – breaking the sound barrier • Means to fly faster than the speed of sound • Plane flying MACH 1 or greater creates a Sonic Boom Watch video Clips: Chuck Yeager breaks sound barrier. Jet breaks sound barrier.

  15. Speed of Sound • Speed can also be measured by multiplying Wavelength by Frequency. • An elephant produces a 10 Hz sound wave. Assuming the speed of sound in air is 345 m/s, determine the wavelength of this infrasonic sound wave. • Humans can detect frequencies as high as 20,000 Hz. Assuming the speed of sound in air is 345 m/s, determine the wavelength of the sound corresponding to the upper range of audible hearing.

  16. Fourier Making Waves Sim • http://phet.colorado.edu/simulations/sims.php?sim=Fourier_Making_Waves

  17. Answer the following Conclusion Questions • What is sound? • What kind of wave does sound travel as? • What affects how sound travels? • What are the four parts of a wave? • What characteristic of sound does frequency determine? • What characteristic of sound does amplitude determine? • Compare ultrasonic to infrasonic. • Describe the Doppler Effect.

  18. Summary • Sound energy comes from the vibration of matter • Sound waves are compressional waves with a region of condensation and a region of rarefaction • Waves consist of four parts; wavelength, period, amplitude, and frequency • Frequency determines pitch, measured in Hertz • Amplitude determines loudness or intensity measured in Decibels. • Doppler effect is due to a change in pitch as a sound passes a receiver • The speed of sound depends on the medium and the temperature.

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