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 on the way.  The study of sound is known as [[acoustics]].  Humans detect sound waves through their [[ears]].

'''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]].

[[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.]]

== Human Perception ==

== Human Perception ==

Sound is caused by the vibration of an object and its effect is a phsiological occurrence in the brain, which also may occur to some extent when reading words or music. The vibration causes waves in air, water, or other object which are detected by the ear. The effect of written and physical sound is affected by the organisms ability to hear it. <ref name="Stevens & Warshofsky Chapter One"> Stevens, S., Warshofsky, F., & others. 1965. ''Sound and Hearing.'' Chapter one. Life Science Library, Time-Life Books, New York, NY: Time, Inc.</ref>  

Sound is caused by the vibration of an object, and its effect is a physiological occurrence in the brain, which also may occur to some extent when reading words or music. The vibration causes waves in a medium which are detected by the ear. The effect of written and physical sound is affected by the organisms ability to hear it. <ref name="Stevens & Warshofsky Chapter One"> Stevens, S., Warshofsky, F., & others. 1965. ''Sound and Hearing.'' Chapter one. Life Science Library, Time-Life Books, New York, NY: Time, Inc.</ref>  

== Sound Wave Propagation ==

== Sound Wave Propagation ==

Scientist Robert Boyle had a bell in a glass jar which contained a vacuum and he could not hear the bell until there was air in the jar. The vibrating object pushed air molicules. Compression is when the molecules bump together. Rarefaction is when they bounce apart, causing the bave to move away from the vibrating object. Marin Mersenne timed echoes to determine that sound travels at 1,038 feet per second. William Derham watching and listening for a cannon boom determined that sound energy traveled at 1,135 feet per second. Others determines that sound moves faster when the air is warmer. <ref name="Stevens & Warshofsky Chapter One" />

Scientist Robert Boyle had a bell in a glass jar which contained a vacuum, and he could not hear the bell until there was air in the jar. The vibrating object pushed air molecules. '''Compression''' is when the molecules bump together. '''Refraction''' is when they bounce apart, causing the wave to move away from the vibrating object. Marin Mersenne timed echoes to determine that sound travels at 1,038 feet per second. William Derham, watching and listening for a cannon boom, determined that sound energy traveled at 1,135 feet per second. Others determined that sound moves faster when the air is warmer. <ref name="Stevens & Warshofsky Chapter One" />

The higher the compression (or sound wave) the louder the sound. The distance between the waves determines the pitch or note. The faster the vibration is, the higher the frequency of the waves, the higher the pitch, note or voice is. <ref name="Stevens & Warshofsky Chapter One" />  

The higher the compression (or sound wave), the louder the sound. The distance between the waves&mdash;known as '''frequency'''&mdash; determines the pitch or note. The higher the frequency of the waves, the higher the pitch is. <ref name="Stevens & Warshofsky Chapter One" />  

When sound waves bump into each other, the resulting waves are fidderent than the original waves. For example, when two equivalent waves are in phase, they occur at the same time and add to each other causing the sound to be louder, but when the equivalent waves are out of phase or inbetween each other they cancel each other out and there is scilence. <ref name="Stevens & Warshofsky Chapter One" />

When sound waves bump into each other, the resulting waves are different than the original waves. For example, when two equivalent waves are in phase, they occur at the same time and add to each other causing the sound to be louder, but when the equivalent waves are out of phase or in between each other they cancel each other out and there is silence. <ref name="Stevens & Warshofsky Chapter One" />

A vibrating tuning fork produces one tone (pure tone). A pure tone is graphed as a sine wave, shaped line an s. Pythagoras pointed out that the longer the string of the same tightness, the lower the note. Fourier claimed the string produces several higher tones (overtones, harmonics) in harmony with the main note of the string, because of vibration waves going along the length of the string. <ref name="Stevens & Warshofsky Chapter One" />

A vibrating tuning fork produces one tone (pure tone). A pure tone is graphed as a sine wave, shaped like an "s". [[Pythagoras]] pointed out that the longer the string of the same tightness, the lower the note. Fourier claimed the string produces several higher tones (overtones, harmonics) in harmony with the main note of the string, because of vibration waves going along the length of the string. <ref name="Stevens & Warshofsky Chapter One" />

When one of two tuning forks of the same size is struck, the other begins to vibrate also. This is an example of resonance or sympathetic vibration. The body of a violin affecting the sound of the violin is also. <ref name="Stevens & Warshofsky Chapter One" />

When one of two tuning forks of the same size is struck, the other begins to vibrate also. This is an example of resonance or sympathetic vibration. The body of a violin affecting the sound of the violin is also. <ref name="Stevens & Warshofsky Chapter One" />