Sound in different media

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1. Sound in Different Media

2. Speed of Sound and Density Sound waves can travel through other materials besides air. The speed in which sound travels in a given highly depends on the density of the medium. In fact, sound is usually fastest in solids where its atoms or molecules are closest together, and slowest in gases where molecules are farthest apart.

3. Speed and Elasticity The elasticity of a material also affects the speed of sound . The elastic property of a material refers to its tendency to maintain its shape and not deform when a force is applied to it. Rigid materials such as steel will experience a smaller deformation than rubber when a force is applied to it because rubber is more flexible. Elastic materials vibrate at lower speeds because their particles return to their original positions at lower rates. Thus, sound travels very slowly in elastic materials than rigid materials. In fact, these types of materials, such as rubber, can be used for soundproofing.

4. Speed and Temperature Sound travels faster if it is hotter. As a substance heats up, its molecules move faster, so they collide more frequently. The more frequent the collisions are the faster the speed of sound is in material. The speed of sound in an ideal gas v, for example, in a given temperature T in Kelvin is given by: v = v o (Equation 1) where v o is the speed of sound at absolute temperature T o .  

5. For air, the speed of sound in air can be approximated using the equation: v = 331 m/s + (0.606 ) T c (Equation 2) w here T c is the temperature of the air in °C. For every 1 ° C rise in temperature, the speed of the air increases by 0.606 m/s. Other factors such as humidity and pressure, can also affect the speed of sound in air.  

6. Example 1. What is the speed of sound in helium at 20°C? The speed of sound in helium at 0°C is 972 m/s. Given: Tc = 20.0°C Solution: Using the speed of sound in helium at 0°C, you have: v = v o = = 972 m/s = 1,010 m/s Answer: Sound travels in helium at 20°C at a speed of 1, 010 m/s.  

7. Example 2 . A thunder was heard by Frandon exactly 5.00 seconds after a lightning flashed. Assuming that the temperature of the air was equal to 26.0°C, how far was the lightning? Given: T c = 26.0°C T = 5.00 s Solution: To determine how far the source of sound is, you need to get first the speed of sound at 26.0°C.

8. v = 331 m/s + T c v = 331 m/s + 26.0°C v = 331 m/s + 15.756 m/s = 347 m/s Thus, the distance of the lightning from Frandon is: d = vt = 347 m/s x 5.00 s = 1,740 m Answer: Frandon is 1,740 m away from the lightning.  

9. Thank You!