1. Chapter 12
Sound Waves

2. Sound is created by a vibrating object setting nearby molecules into motion.
Molecules are either pushed together (compressed) or not (rarefracted).
This vibration creates a longitudinal wave which can be translated into a sine wave to show frequency, amplitude and wavelength.

3. The frequency of an audible sound wave determines how high or low a pitch we hear.
With our penny drop...low pitch=low frequency while high pitch=high frequency. The material of which the pennies were made create different frequencies as they strike the table and vibrate the air around them.

4. Pitch depends on a few factors:
Frequency
Loudness
Background noise or interference

5. As we learned before, speed of sound depends on the medium which the vibration is traveling through.
Look at the table on page 410!!!
Why does sound travel faster in a solid than in a gas?
Why does sound travel faster in warm air than cool air?

6. Contrary to what th last chapter said, sound DOES TRAVEL in 360° from the vibration source!!!
As we learned before, light travels about 1,000,000 times faster than sound!!!

7. Can you really measure distance using lightening and thunder?

8. YES!!!!!
Count from flash to crash / 5 = x miles

9. Sound Intensity
Intensity is the rate of energy flow through a space or area.
Intensity = P/4πr (watts/squared meters)

10. Example 1:
What is the intensity of a sound wave produced by a trumpet at a distance of 3.2 m when the power output is measured at 0.20W?

11. Intensity and frequency determine which sounds are audible.
Relative intensity is measured in decibels.

12. Homework…
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