2. Sound Ch 26

3. What is sound?  All sound waves are produced from some sort of vibration  Sound is a series of compressions and rarefactions causing inner parts of your ear to vibrate  Compression- when the vibrating object moves toward the medium forcing the medium closer together  Rarefaction- when the vibrating object moves away from the medium allowing the medium to spread apart

4. Sound needs a medium to travel through  Normally this is air, but it can be anything  Imagine all the atoms and molecules of the medium (the area surrounding the source of the sound) to be like people in a VERY crowded area.  If one person is pushed a wave of energy is sent through the entire crowd. That’s a sound wave.

5. Compressions/rarefactions

6. What do sound waves look like  Sound waves are longitudinal waves, meaning the medium moves parallel to the direction of wave propagation. {as opposed to transverse where the medium moves perpendicular to the way the wave is going}  Sound waves travel in all directions three dimensionally from the source  To represent this two dimensionally on paper, we draw circles around the source, with each circle representing a sphere

7. The representation

8. What we can hear  Audible Sound Waves (sound we can hear) on average have frequencies ranging from 20 Hz to 20,000 Hz  Every human ear is different and changes with age. So the frequencies you can hear may vary.  Frequency of sound waves are what we hear as pitch  High frequency sounds give high-pitched sounds (like a screech)  Low frequency waves give low-pitched sounds (like a bass beats)

9. Homework  Pg 528 1-10