2. Sound surrounds us all the time. Throughout the day we hear many kinds of sounds, such as the clatter of pots and pans, the roar of traffic and the voices of people.

3. All the sounds we hear have one thing in common. Every sound is produced by vibrations of an object. When an object vibrates, it makes the surrounding air vibrate/ The vibrations in the air travel outward in all directions from the object. Sound has a great importance in our lives.

4. Sound also travels in waves as it moves through the air or some other medium (substance). The waves are produced by a vibrating object. As a vibrating object moves outward, it compresses the surrounding medium, producing a region of compression called condensation.

5. As the vibrating object then moves inward, the medium expands into the space formerly occupied by the object. This region of expansion is called a refraction. As the object continues to move outward and inward, a series of condensations and refractions travels away from the object. Sound waves consist of these condensations and refractions.

6.  A disturbance consisting of condensations and refractions.

8.  Acoustics  Beats  Condensation  Decibel  Frequency  Hertz  Infrasound  Intensity  Phon  pitch  Refraction  Resonance frequency  Sound quality  ultrasound

9. The intensity of a sound is related to the amount of energy flowing in the sound waves. Intensity depends on the amplitude of the vibrations producing waves. Amplitude is the distance that a vibrating object moves from its position of rest as it vibrates.

10. Sound quality also called timbre, is a characteristic of musical sounds. Quality distinguishes between sounds of the same frequency and intensity produced by different musical instruments.

11. Scientists use a unit called decibel to measure the intensity level of a sound. A 3,000-hertz tone of zero decibels marks the threshold of audibility. A sound intensity of 140 decibels is the threshold of pain.

12. The properties of a medium that determine the speed of sound are density and compressibility. A plane flying faster than the speed of sound creates shock waves, strong pressure disturbances that build up around the aircraft. People on the ground hear a loud noise known as a sonic boom.