Sound is a kind of a vibration created in a medium. So let us first mention a few things about vibration. Everything in nature vibrates by itself although in most cases the vibrations are too small or too fast for us to detect. Such vibrations are called natural or free vibrations. Vibrations can also be caused by the repeated use of some external force. Such vibrations are known as forced vibrations. Vibrations are normally measured by their frequencies, i.e. The number of cycles completed per unit of time, or by their wavelengths, i.e. The distance between any point on one wave and the corresponding point on the next one. As the frequency increases, the wavelength goes down. But there is another important aspect of the wave to consider is the amplitude i.e. The distance a vibrating object moves from its position of rest. The larger the amplitude, the higher would be the intensity or the amount of energy flowing in the vibration. So a vibration with a very high amplitude can contain energy high enough to break a glass.
