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Natural Frequency A vibrating object is the source of any disturbance that moves through a medium that we call 'sound'. The frequency or frequencies at which an object tends to vibrate when 'somehow disturbed' is known as the natural frequency of the object. 'Somehow disturbed' may mean hit, plucked, strummed, blown through (or across), pinged - anything that might set vibrations into operation. When an object vibrates, it vibrates at a particular frequency or a set of frequencies. If the amplitude of the vibrations are large enough (and if natural frequency is within the human frequency range), then the vibrating object will produce sound waves that are audible and often memorable. It is how you can identify objects you have bumped into or dropped! Types of sound producedThe quality or timbre of the sound produced by a vibrating object is dependent upon the natural frequencies of the sound waves produced by the objects. Some objects tend to vibrate at a single frequency and are said to produce a 'pure tone'. A flute tends to vibrate at a single frequency, producing a very pure tone. Other objects vibrate and produce more complex waves with a set of frequencies that have a whole number mathematical relationship between them; these are said to produce a 'rich sound'. A tuba tends to vibrate at a set of frequencies that are mathematically related by whole number ratios; it produces a rich tone. Objects that vibrate at multiple frequencies that have no simple mathematical relationship between them are not musical in the sounds they produce and the sounds that they create could be described as 'noise'. When a pencil is dropped on the floor, it vibrates with a number of frequencies, producing a complex sound wave that is clanky and noisy.
If you apply a forced vibration at the natural frequency of an object it resonates. |
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Cyberphysics - a web-based teaching aid - for students of physics, their teachers and parents....
