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Sound

Sound. Speed of sound in solids, liquids, and gases. Speed of sound in gas (air): 344 m/sec. Speed of sound in liquid (water): 1100 m/sec Speed of sound in solid (steel): 5000 m/sec Speed of sound wave dependenton strength of bonds between atoms.

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Sound

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  1. Sound

  2. Speed of sound in solids, liquids,and gases • Speed of sound in gas (air): 344 m/sec. • Speed of sound in liquid (water): 1100 m/sec • Speed of sound in solid (steel): 5000 m/sec • Speed of sound wave dependenton strength of bonds between atoms. • Why is helium so high and what is an example of this high speed

  3. Temperature dependence of sound speed • Speed dependent on temperature • For liquids and gases speed increases for increasing temperature. • One experiment to measure global warming is to measure speed of sound in oceans. • Warmer oceans will result in slightly faster speed.

  4. Speed of sound and sonic boom • Plane moves through sound waves and creates a shock wave or “sonicboom”.

  5. Intensity of sound • An explosion or other sound producer such as a rock produces power. Units are Watts (W). • Intensity (I) is a measure of the loudness of the sound a distance from the source. Units are W/m2 • The intensity decreases with the square of the distance from the source.

  6. Intensity • Intensity and Distance • Example: At a distance of 10 m from source a sound has an intensity of 100 W/m2 • What is intensity at a distance of 50 m? • (10/50)2 = 1/25 = 0.04 • I = 100 *0.04 = 4 W/m2

  7. Examples of sound intensity For each example a person is 1 m from source. • A Saturn rocket has a power 50,000,000 W • compared to: 0.0000000000001 W for the threshold of hearing. • Decibel scale- measures sound intensity, based on log scale (powers of 10)

  8. Changes in intensity and dB. • Question. How does a 80 dB compare to 70 db sound? • 10 dB means 10 times louder. • Question. How does a 80 dB compare to 60 db sound? • 20 dB means 10 x 10 = 100 times louder. • Question. How does a 80 dB compare to 50 db sound? • 30 dB means 10 x 10 x 10 = 1000 times louder. • Question: If a sound intensity is doubled from • 1 W (120 dB) to 2 W what is the new dB? • 123 dB (change in 3 dB).

  9. Frequency and pitch • Pitch is how high or low the sound is (not loud or soft) Pitch is dependent on vibrations per second or frequency Humans can hear a range between 20-20000Hz Above 20000Hz is called ultrasonic – above our abilty to hear Timbre – refers to the quality of sound

  10. Hearing • Infrasonic –frequencies below 20Hz • Ultrasonic –frequencies above 20000Hz • So intensity is Amplitude • Pitch is Frequency

  11. Echoes and Reverberation • Echoes and Reverberation • Echo – reflection of sound. • Reverberation – multiple reflection in a small area • SONAR – SOund NAvigation and Ranging • Uses an echo to determine distance

  12. Doppler effect • A change in frequency and pitch due to either motion of the observer or object

  13. Resonance • Adding energy at just the right frequency to get the amplitude to increase. • Example: breaking a crystal glass

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