sound

=Sound= **definitions and examples of:**
 * Speed of sound
 * Vibration and pitch
 * Echoes
 * Doppler effect
 * Resonance

Speed of sound;
speed of sound is the distance travelled during a unit of time by a sound wave. 'In dry air at 20 °C (68 °F), the speed of sound is 343.2 metres per second (1,126 ft/s). This is 1,236 kilometres per hour (768 mph), or about one kilometer in three seconds or approximately one mile in five seconds.' **Vibration and pitch;** Vibration is what makes sound travel, the sound vibrates which makes it travel, the more energy the further the sound will travel. The pitch is how low and how high the sound or frequency is.

Echoes;
A sound  thats been repeatedby the reflection of sound waves from a wall, mountain,  or other obstructing surface.

Doppler effect;
An increase or decrease in the frequency of sound, light, or other waves as the source and observer move toward each other. media type="youtube" key="ZPJyYaXhuv4" width="425" height="350"