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02 – Speed of Sound & Mach Numbers

Unit 4 - Sound. 02 – Speed of Sound & Mach Numbers. Speed of Sound. Sound is much slower than light For Example: When you see lightning in the sky, the sound (thunder) takes a few seconds to reach you. Speed of Sound. The speed of sound depends on two important factors: Pressure

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02 – Speed of Sound & Mach Numbers

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  1. Unit 4 - Sound 02 – Speed of Sound & Mach Numbers

  2. Speed of Sound • Sound is much slower than light • For Example: • When you see lightning in the sky, the sound (thunder) takes a few seconds to reach you

  3. Speed of Sound • The speed of sound depends on two important factors: • Pressure • Temperature • The speed of sound in air at 0°C and normal atmospheric pressure is 332 m/s • If the pressure stays constant, as the temperature increases, the speed of sound increases by about 0.6 m/s for each degree Celsius • Formula to determine the speed of sound: • Speed of sound = (332 + 0.6T) m/s • Where T is temperature in °C.

  4. Calculating Speed of Sound • Example 1: • What is the speed of sound at 15°C? • v = 332 + 0.6T m/sv = 332 + 0.6(15) m/sv = 332 + 9 m/sv = 341 m/s

  5. Calculating Speed of Sound • Example 2: • What is the speed of sound at -14°C? • v = 332 + 0.6T m/sv = 332 + 0.6(-14) m/sv = 332 + (-8.4) m/s v = 324 m/s

  6. Different Media • The speed of sound varies in different materials • Generally the speed of sound is greater in solids and liquids than in gases, although there are a few exceptions. • When calculating the speed of sound in different media, simply change the “332” to the appropriate value

  7. Different Media * depends on salinity and depth

  8. Mach Number • Aircraft traveling at high speeds often have their speeds given as a Mach Number rather than kilometers/hour or m/s • Mach number is the ratio of the speed of an object to the speed of sound • The speed of sound at sea level and 0°C is 332 m/s or about 1200 km/h • At an altitude of 10 km, the speed of sound is about 1060 km/h.

  9. Mach Number Examples: • 1. What is the Mach number of an aircraft traveling at sea level at 0°C with a speed of 2400 km/h? • Mach number = speed of object speed of sound • Mach number = 2400 km/h 1200 km/h • Mach number = 2.0

  10. Mach Number Examples: •  2. What is the speed of an aircraft flying at Mach 1.5 if it is flying at an altitude of 10. km? • Mach number = speed of object speed of sound • speed of object = Mach number (speed of sound) • speed of object = 1.5(1060 km/h) • Speed of object = 1.6 x 103 km/h

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