1. Unit 4 - Sound

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/s v = 332 + 0.6(15) m/s v = 332 + 9 m/s v = 341 m/s

5. Calculating Speed of Sound  Example 2: What is the speed of sound at -14°C? ○ v = 332 + 0.6T m/s v = 332 + 0.6(-14) m/s v = 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 SubstanceSpeed at 0°C in m/s carbon dioxide258 oxygen317 air332 lead1200 alcohol1241 hydrogen gas1270 sea water1500 * fresh water1500 copper3560 maple wood4110 steel5050 aluminum5104 * 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 10 3 km/h