2.  Sound is a longitudinal wave created by a vibrating object.  Sound is a mechanical wave.  PhET Simulation PhET Simulation  Demo: Standing Sound Waves

3.  Subtle compressions and rarefactions in the air cause our ear drums to vibrate. The auditory nerve sends a signal to the brain, which perceives these vibrations as the sounds we hear.

4.  We hear differences in…

5.  SOUND INTENSITY is the perceived loudness of a sound. It is affected by the AMPLITUDE of the vibrations.  Sound intensity is measured in decibels (dB).

6. The decibel scale is a logarithmic scale based on powers of 10. That means if you increase the intensity by 10dB the intensity doubles. So, 130 dB is TWICE as loud as 120 dB.

7. 140 dB jet plane, gun shot 120 dB pneumatic drill, clap of thunder(pain threshold) 100 db music on earphones at standard volume level, car horn from 5m away, factory machinery 90 dB lawnmower, subway train 85 dB level at which ear damage may begin 60 dB normal conversation 20 dB whisper, ticking of a watch 10 dB breathing 0 dB threshold of hearing

8.  The pitch (highness or lowness) of a sound is determined by the frequency of vibrations.  DEMO: What frequencies can you hear?

9. The general range for human hearing is 20 to 20,000 Hz. Sounds that have frequencies below 20 Hz are called INFRASONIC. Sounds that have frequencies above 20,000 Hz are called ULTRASONIC.

10. The Doppler Effect When an sound source is moving, the frequency (pitch) perceived by the observer changes. http://www.colorado.edu/physics/2000/appl ets/doppler2.html http://www.walter- fendt.de/ph14e/dopplereff.htm

11. v=331 m/s at STP v= 343 m/s at 20˚ C (room temperature) Factors that affect the speed of sound: Density Temperature

12.  Objects that travel faster than the speed of sound are SUPERSONIC.  Mach number describes how much faster than the speed of sound the object travels.  Mach 3 = 3x the speed of sound.  Objects traveling at a speed greater than Mach 5 are HYPERSONIC.

13. Breaking the sound barrier…

14. https://www.youtube.com/watch?v=gWGLAAYdbbc