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Properties of Sound

What is Sound?

Sound is the motion of particles in a medium, caused by a vibrating source that stimulates the auditory nerve in the human ear.

Every sound wave originates from a vibrating source. The average human is responsive to frequencies between 20 Hz and 20 000 Hz. Frequencies above 20 000 Hz are called ultrasonic and those below 20 Hz are called infrasonic.
Vibrating sources may be vocal cords, vibrating strings, resonating air columns or objects being struck together.
Sounds that are unpleasant are called noise.
All sources of sound produce condensations and rarfactions that travel to the ear and are "heard".
Sounds have quality, intensity, & pitch or frequency. See chart on right.

Sound Clip
Sound Clip
Sound Clip
Sound Clip
Sound Clip
Sound Clip
 Different Frequencies of Sounds

Speed of Sound

In 1738, members of the French Academy were first to measure the speed of sound. By measuring the time between the flash of a cannon and the boom, the speed of sound was measured.

Speed of Sound Formula

Note:
The speed of sound varies in different substances. It is determined mostly by the type of medium.
The speed of sound is greater in solids and liquids than in gases.

The speed of sound at sea level and zero degrees Celsius is 332 m/s, or approximately 1200 km/h.
If a person was to say "hello" to a friend across a 332 m body of water, the friend would hear the greeting one second after the actual word was said.


Example of the Speed of Sound

Mach Number

Mach Speeds Formula

The high speeds of a supersonic aircraft are given in Mach numbers. The Mach number is based on the speed of sound. Mach 1 is the speed of sound, Mach 2 is two times the speed of sound, etc...


Stealth Bomber


The Stealth Bomber is an example of a jet that travels at speeds greater than Mach 1.







Notes to be Taken

  1. Where do sounds come from and what is the auditory frequency the average person can detect?
  2. What is meant by "quality of sound"?
  3. What is the speed of sound at
    1. 0.0 oC
    2. 23.5 oC
    3. -12.4 oC
  4. Define what a Mach Number is.
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