Sound is produced by vibrations of material objects.  Sound is a longitudinal wave.  It needs a medium to travel trough.  Remember from chapter 14 that a longitudinal wave is a wave that vibrates parallel to the motion of the wave. 

Before we start taking too much about tuning forks, it is important to know about them and how to properly handle them!  Watch the video to find out more!

Your voice is produced by vibrations from your vocal cords.  Your vocal cords vibrate, which in turn, vibrates the particles next to your vocal cords, then the particles next to those start vibrating, and so on until the particles right next to your eardrum start vibrating, which vibrates your eardrum.  

Sound waves can move through air, liquids, and solids.  Sound cannot move through a vacuum. In a vacuum, there are no particles to vibrate and transmit the sound.

Do you ever wonder why your voice sounds differently on a recording than how we hear it normally?  hate to tell you this, but how you hear your voice on a recording is the same that everyone else hears it!  

Watch this video to see why!

Forced vibration is the vibration of an object that is made to vibrate by another vibrating object that is nearby.  That is how sound travels.  One molecule starts to vibrate then it forces the molecule next to it to vibrate and so on and so on.

Watch the video for a quick demonstration of forced vibration using sympathetic tuning boxes.

The speed at which sound travels from one place to another depends upon the medium and how closely packed the molecules are in the matter.  Where there is no medium, no sound can be transmitted.  Of the three mediums (solid, liquid, and gas), sound waves travel the slowest through gases, faster through liquids, and fastest through solids.

The closer together the molecules are, the faster that they can transmit the sound.

Sound is much slower than light.  This is why we hear thunder after you see a flash of lightning.  

The speed of sound in air is different when the air is at different temperatures.  The speed of sound increases as the temperature increases.

The speed of sound in air depends on the temperature, with the speed increasing by about 0.6 m/s for each 1ºC increase in air temperature.  At room temperature, (20ºC) sound moves through air at sea level at a speed of 343 m/s.

The speed of sound in a material does not depend on the materials density, but on its elasticity.  Elasticity is the ability of a material to change in shape in response to an applied force, then resume its initial shape once the distorting force is removed.

Steel is very elastic, like tuning forks.  Putty or play dough, is very inelastic.  In elastic materials the atoms are relatively close together and respond quickly to each other's motions, transmitting energy with little loss.

When any object composed of an elastic material is disturbed, it vibrates at its own special set of frequencies, which together form its special sound.  Natural frequency is the frequency at which an elastic object, once energized, will vibrate.

Click the video to watch a great animation on how sound travels.

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