Perhaps you have seen a pendulum bob vibrating back and forth about its equilibrium position. While a pendulum does not produce a sound when it oscillates, it does illustrate an important principle. A pendulum consisting of a longer string vibrates with a longer period and thus a lower frequency. Once more, there is an inverse relationship between the length of the vibrating object and the natural frequency at which the object vibrates. This very relationship carries over to any vibrating instrument - whether it is a guitar string, a xylophone, a pop bottle instrument, or a kettledrum.or turntable chassis ,objects have a natural frequency or set of frequencies at which they vibrate when struck, plucked, strummed or somehow disturbed. The actual frequency is dependent upon the properties of the material the object is made of (this affects the speed of the wave) and the length of the material (this affects the wavelength of the wave). It is the goal of musicians to find instruments that possess the ability to vibrate with sets of frequencies that are musically sounding (i.e., mathematically related by simple whole number ratios) and to vary the lengths and (if possible) properties to create the desired sound