When sound waves move through the air, each air molecule vibrates back and forth, hitting the air molecule next to it, which then also vibrates back and forth. When the vibrations are fast (high frequency), you hear a high note. When vibrations are slower, you hear a lower note.

 

When we hear something, we are sensing the vibrations in the air. The number of vibrations per second is known as the frequency, measured in Hertz (1 Hz = 1 vibration per second). The fastest vibration we can hear is 20,000 times per second, which would be an extremely high sound. Animals can hear different frequencies from humans. 

 

In the same medium, all sound waves travel at the same speed.  Consequently, a sound wave can only propagate through a limited distance. In general, low frequency waves travel further than high frequency waves because there is less energy transferred to the medium.  Sound travels more slowly than light. Sound waves travel at the same speed but vibrate in different ways. Some vibrate quickly and have a high frequency or pitch, while others vibrate slowly and give a lower pitch.

 

The speed of sound is dependent on temperature. As the temperature of the air increases, the speed of sound in air increases.  Frequency of sound and pitch are related. The higher the pitch, the greater the frequency.  Amplitude is a measure of the size of sound waves. It depends on the amount of energy that started the waves. Greater amplitude waves have more energy and greater intensity, so they sound louder. As sound waves travel farther from their source, the more spread out their energy becomes.