Changes

'''Sound''' is a disturbance caused by variations in [[pressure]] that travels as longitudinal [[waves]] through a [[medium]] such as air or water, disturbing molecules along the way.  The study of sound is known as [[acoustics]].  Humans detect sound waves through their [[ears]]. When a twig breaks, it pushes the air molecules. Sound waves get weaker as they expand, while they are moving away from the source of the sound. A longer wavelength has a lower frequency since the waves come less often than a high frequency. Rarefaction is the low pressure part of the sound wave while compression is the “pushing” part of the wave. A changing distance to the object generating the sound affects the frequency and pitch; this is the Doppler effect.<ref name="Science Service">Science Service, Science Program. 1968. ''Sound and Hearing.'' USA: Nelson Doubleday, Inc. and Odhams Books Ltd.</ref>

'''Sound''' is a disturbance caused by variations in [[pressure]] that travels as longitudinal [[waves]] through a [[medium]] such as air or water, disturbing molecules along the way.  The study of sound is known as [[acoustics]].  Humans detect sound waves through their [[ears]]. When a twig breaks, it pushes the air molecules. Sound waves get weaker as they expand, while they are moving away from the source of the sound. A longer wavelength has a lower frequency since the waves come less often than a high frequency. Rarefaction is the low pressure part of the sound wave while compression is the “pushing” part of the wave. A changing distance to the object generating the sound affects the frequency and pitch; this is the Doppler effect.<ref name="Science Service">Science Service, Science Program. 1968. ''Sound and Hearing.'' USA: Nelson Doubleday, Inc. and Odhams Books Ltd.</ref>

Sympathetic vibrations of an object are caused by sound and are at the object’s resonance frequency. A violin string’s harmonics, or various vibrations, produces its timbre or specific sound. The harmonics include the fundamental frequency and the overtones. Some sounds interfere with other sounds resulting in different sounds. High frequencies are absorbed first by a rough surface such as the walls of an anechoic chamber. A hard, smooth surface reflects sound. Reverberations are sound reflections arriving almost with the direct sound, like in a room. Echoes are sound reflections from farther away. They arrive more after the direct sound does, like in a canyon. Some sound diffracts around things.<ref name="Science Service" />

Sympathetic vibrations of an object are caused by sound and are at the object’s resonance frequency. A violin string’s harmonics, or various vibrations, produce its timbre or specific sound; the harmonics include the fundamental frequency and the overtones. Some sounds interfere with other sounds, resulting in different sounds. High frequencies are absorbed first by a rough surface such as the walls of an anechoic chamber. A hard, smooth surface reflects sound. Reverberations are sound reflections arriving almost with the direct sound, like in a room. Echoes are sound reflections from farther away. They arrive more after the direct sound does, like in a canyon. Some sound diffracts around things.<ref name="Science Service" />

A bat’s brain navigates in total darkness using the echos of the bat’s chirps, which are too high in pitch for humans to hear. The higher the sound wave frequency, the higher the note. However, changes in frequency do not match precisely changes in pitch, so musical instruments are basically tuned by ear. Sound wave strength or intensity also does not match what it sounds like. Therefore, while intensity is measured in microbars, the loudness it causes is measured in decibels. Some kinds of jet engine are quieter than others and Santa Barbara, California was the first U.S. city to outlaw sonic booms.<ref name="Science Service" />

A [[bat]]’s brain navigates in total darkness using the echos of the bat’s chirps, which are too high in pitch for humans to hear. The higher the sound wave frequency, the higher the note. However, changes in frequency do not match precisely changes in pitch, so musical instruments have to be tuned by ear. Sound wave strength or intensity also does not match what it sounds like. Therefore, while intensity is measured in microbars, the loudness it causes is measured in decibels. Some kinds of jet engine are quieter than others and Santa Barbara, California was the first U.S. city to outlaw sonic booms.<ref name="Science Service" />

[[Image:Varma Lady with Sitar.jpg|thumb|left|Lady with Sitar by Ravi Varma.]]

[[Image:Varma Lady with Sitar.jpg|thumb|left|Lady with Sitar by Ravi Varma.]]