ch26_ccjp

=Chapter 26 - Sound= = =

The Origin of Sound:
The origin of sound is the vibration of the object, because vibrations produce the sound. Under ordinary conditions, the frequency of the vibrating source equals the frequency of sound waves produced.

Ex: A violin produces sound through vibrating strings. These vibrating strings trigger the sound board of the violin, creating beautiful notes through the f-holes.

**Pitch**- The subjective impression about the frequency of sound; high-pitched sound=high vibration frequency, low pitch sound=low frequency (proportional)
 * Infrasonic**- Sound waves with frequencies below 20 hertz (hearing range)
 * Ultrasonic-** Sound waves with frequencies above 20,000 hertz

**Sound in Air:**
Compression- A pulse of compressed air, when there is a disturbance in the air, molecules are pushed over. They push other molecules over and so on. This is called compression. Rarefaction- Air in a low-pressure zone, rarefactions follow compressions []

**Media that Transmit:** Sound travels through solids, liquids, and gasses. Sound is transmitted faster in liquids than in gasses, ands still faster in solids. Sound must be transmitted through a medium because the medium allows sound waves to compress and expand. If the sound waves cannot expand and compress there can be no sound.

FYI: Sound cannot transmit through space!
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**Speed of Sound:**
Sound is slower than light. Increased temperature increases the speed of sound. The speed of sound travels in dry air at (0 degrees Celcius) 330 m/s. At room temperature (20 degrees Celcius) 340 m/s. For each degree increase, the speed increases by .6 m/s.
 * Loudness:** Measured by a tool called the oscilloscope. Psychological sensation, and therefore subjective. Related to intensity of sound. Measured by decibel (dB).

Forced Vibrations:

 * Forced vibration** is when matter is forced to vibrate. For example, when a tuning fork is struck and placed against a tabletop, the tapletop is forced to vibrate. The sound of the tuning fork on the table is greater than the tuning fork unmounted.

Natural Frequency:
Different objects vibrate at different natural frequencies. Natural frequency is when the most minimal amount of energy is used to make a forced vibration.

Resonance:

 * Resonance** is when the frequency of a forced vibration on an object matches the object's natural frequency, a dramatic increase in amplitude ocurs. When tuning forks are set in a row, the first in the line to vibrate sets the next into vibration and so on. This is an example of how the tuning forks resonate and cause forced vibration The forks must be adjusted for matched frequencies otherwise the resonance will not occur. There are some problems with resonance and natural frequency. When an infantry marched over a bridge in 1831, they marched at the bridge's natural frequency which caused the bridge to collapse. Today, when troops cross a bridge they break step so the bridge won't collapse.

Interference:
Sound waves can be made to interfere. Constructive interference: The crest of one wave overlaps the crest of another wave; amplitude increases. Destructive interference: The crest of one wave overlaps the trough of another wave; aplitude decreases.

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The crest of a wave correspondes to compression The trough of a wave correspondes to refraction Interference occurrs in longitudinal and transverse waves

Beats: Beat: Periodic interference in the loudness of sound. The interference of two sound sources of slightly different frequency produce beats Beats are made up of constructive and destructive interference. People can use beats to tune instruments

Ex: Think of two overlapping small tooth combs. The unequal spacing between the teetch create a patter similar to the patter of constructive and destructive frequencies that make up beats.