1. Sound
13.2

2. Sound Intensity Intensity is the rate of energy flow through an area.
With sound intensity we want to know the rate of energy flow through a plane wave.

3. Formula Intensity = __P___ 4πr2 Intensity = ________Power__________
4π(distance from the source)2

4. Intensity vs Frequency
Intensity and Frequency determine which sounds are audible. Sounds at low frequencies must have a high intensity to be heard.
The threshold of hearing is the softest a sound can be for human hearing Hz and 1.0 x W/m2.
The threshold of pain is 1.0 W/m2. This is the most intense sound can be without causing pain.

5. Relative Intensity
Intensity is not directly related to volume (loudness).
Relative Intensity is determined by relating the intensity of a sound wave to the intensity at the threshold of hearing. It is related to loudness and is measured in decibels (db).

6. Decibel Levels Volume (Loudness) doubles with every 10 db. Ex:
0 db= threshold of hearing
30 db= whisper
50 db= normal conversation
70 db= vacuum cleaner
90 db= lawn mower
120 db= threshold of pain

7. Vibrations
Sympathetic Vibration- when a vibrating object causes another object to vibrate.
Ex: Plucked guitar strings vibrate and cause the body of the guitar to vibrate.
Natural frequency- this is the set frequency at which a pendulum (or string) will vibrate and is determined by length.

8. Resonance is a condition that exists when the frequency of a force applied to a system matches the natural frequency of vibration of the system.
Waves Video