1. Cornell Notes 4-2-1-1 Sound Waves
April 9, 2018
Page 153

2. What Are Sound Waves? Sound waves are mechanical waves
The medium sound waves pass through is usually air, although sound also passes more effectively through both liquids and solids
Sound is caused by squeezing air molecules as they travel, so sound waves are compression waves (longitudinal waves)

3. What a Sound Wave Looks Like

4. More on Sound Waves Sound waves are repeating vibrations
Even though the waves are compression waves, it often helps to view a sound wave as a transverse wave.

5. Amplitude
The amplitude of a wave tells you its volume (how loud it is)
More amplitude gives you a louder sound
We measure volume in a unit called decibels (dB)
Decibels is a logarithmic scale – that means 20 dB is ten times as loud as 10 dB, 30 dB is 100 times as loud, and 40 dB is 1000 times as loud

6. Frequency and Wavelength
The frequency of a sound wave determines its pitch (what note it is.)
The higher the frequency, the higher the pitch
This also means that longer wavelengths give lower pitches

7. Frequency in Music
Each octave of notes means double the frequency and half the wavelength
For example, middle C has a frequency of 261 Hertz while High C has a frequency of 522 Hz (C*2) and Low C has a frequency of 130 Hz (C*½)
Likewise, other notes have similar fractions. For example, F has a frequency 4/3 that of C and G has a frequency 3/2 that of C.

8. The Speed of Sound
Please remember that the velocity of a wave is its frequency times its wavelength
For sound this is 343 m/s or 767 mph
This is the speed of sound in air. If you change the medium, you change the speed of the sound – the speed of sound is almost 5 times faster in water!

9. In Space No One Can Hear You Scream
Since sound is a mechanical wave, it needs to travel through a medium
This means sound cannot travel in a vacuum, like space or a vacuum chamber.