1. Sound is produced by vibrating matter.

All sounds are produced by vibrating matter. The vibrations must be in the range of about 20 cycles per second to about 20,000 cycles per second to be heard by humans.

2. Sound is the propagation of longitudinal waves through matter.

When a tuning fork is struck each arm vibrates back and forth. As one arm of the fork moves out it pushes the air in front of it. The air particles receive energy from the tuning fork and are compressed together. This produces a high pressure region called a compression. As this air collides with other particles of air it causes them to be compressed as well. When the tuning fork arm moves back in the other direction, it creates a low-pressure region called a rarefaction. As neighboring particles of air from a compression rush into this low- pressure region, the rarefaction propagates outward from the tuning fork. As the tuning fork continues to vibrate, alternating regions of compression and rarefaction are produced and propagate outwards through the air in all directions. This is a longitudinal wave. The difference between a longitudinal wave and the other kind of wave (such as a water wave) called a transverse wave can easily be shown with a Slinky. With the Slinky held between two people, a flick of the wrist by one will send a transverse wave down the slinky.

To show a longitudinal wave, one person must pull a small number of coils of the slinky toward one end and then release it. This will also produce a wave that travels down the slinky toward the other end. The air particles, as well as the slinky, do not move from one place to another. They just simply vibrate back and forth. It is the wave that moves not the material vibrating.

Waves can be described by their wavelength, amplitude, and frequency. The wavelength is the distance between any point along a wave and the corresponding point on the next wave. The amplitude is the maximum distance the wave moves from its normal position, and the frequency is how many times a second a specific wave moves from its normal position through a complete back-and-forth cycle. The hertz is the unit used to measure frequency.

3. The speed of sound varies depending on the medium through which it is traveling.

Sound generally travels faster through solids, than through liquids or gases. The denser the material, the greater the speed.

4. A variety of different methods is used to cause sound vibrations in musical instruments - striking, plucking, stroking, or blowing.

Usually, musical instruments are grouped into 3 groups: stringed instruments (e.g. piano, guitar, cello, violin), wind instruments (e.g. clarinet, trombone, saxophone, trumpet, organ), and percussion instruments (e.g. drums, cymbals).

5. Pitch (highness or lowness of sound) is related to the frequency of vibrations.

Pitch is related to the number of waves that strike your eardrums each second (frequency), and the way your brain processes this information. Low-pitched sounds send a small number of vibrations to your ear per second, while high-pitched sounds send a larger number of vibrations per second. Humans can generally hear sounds from 20 cycles/second (also called 20 hertz or 20 hz) up to about 20,000 hz. As people grow older, their ability to hear high- pitched sounds diminishes. Sounds below 20 hz are called infrasonic while those above 20,000 hz are called ultrasonic. Bats emit sounds with frequencies of 200,000 hz and use the echoes of these sounds to guide their way!

6. Loudness is related to amplitude of vibrations and the size and/or number of vibrating objects.

Loudness of sound is measured in decibels (db), named after Alexander Graham Bell.  The following table shows the relative loudness of common sounds.

Jet Airplane, 100 feet away -- 140 db
Air raid siren, nearby -- 125 db
Rock music,amplified -- 115 db
Vacuum cleaner -- 75 db
Busy street traffic -- 70 db
Conservation -- 65 db
Whisper -- 20 db
Threshold of hearing -- 0 db. 

7.  Musical sound has tone (harmonic content, quality).

The fundamental frequency is the lowest frequency produced by a vibrating object. The fundamental frequency, and other vibrational modes of the object with frequencies of whole number multiples of this fundamental are called harmonics. The quality of a sound depends on the number of harmonics (also called overtones) and their intensities. The qualities of stringed instruments depend on the mounting of the strings, the method of getting the strings to vibrate, and the characteristics of the sounding boards. In wind instruments, the pitch of the tone is usually that of the fundamental or one of its overtones. In percussion instruments, the fundamental tone depends on the shape, the elasticity, and sometimes (as in drums) the tension of the surface.

8. Resonance is the inducing of vibrations of a natural rate by a vibrating source having the same frequency.