1. Sound Waves
Molecules in the air vibrate about some average position creating the compressions and rarefactions. We call the frequency of sound the pitch.

2. What can sound waves travel through?
Sound is a waveform that travels through matter.
Although it is commonly associated in air, sound will readily travel through many materials such as water and steel.
Some insulating materials absorb much of the sound waves, preventing the waves from penetrating the material.

3. Vibrations & Waves & Sound
“a periodic motion of the particles of an elastic body or medium in alternately opposite directions from the position of equilibrium when that equilibrium has been disturbed”
When things vibrate, they move the air and create sound waves
Music, talking, sirens, etc.

4. Can sound travel though a vacuum?
Because sound is the vibration of matter, it does not travel through a vacuum or in outer space.
When you see movies or TV shows about battles in outer space, you should only be able to see an explosion but not hear it. The sounds are added for dramatic effect.

5. What kind of waves are sound waves?
The back-and-forth vibration of an object creates the compression waves of sound.
The motions of a loudspeaker cone, drumhead and guitar string are good examples of vibration that cause compression waves.
This is different than the up and down or transverse motion of a water wave.

6. Decrease in loudness
A sound wave will spread out after it leaves its source, decreasing its amplitude or loudness.
The amplitude decreases as the square of the distance from the source.
Also, if there is some absorption in the material, the loudness of the sound will decrease as it moves through the substance.

7. Speed or velocity of sound
The speed or velocity of sound in air is approximately 344 meters/second, 1130 feet/sec. or 770 miles per hour at room temperature of 20oC (70oF).
The speed varies with the temperature of air, such that sound travels slower at higher altitudes or on cold days

8. Speed of Sound Depends on the material of the vibrating medium
Sound can vibrate water, wood (speaker enclosures, pianos), metal, plastic, etc.
Sound speed in dry air is 330 meters/second at 0o C
Faster in warm air, slower in cold
Water 4 times faster, steel 15 times faster