SVCAUSA 2010
Resonance

Suppose an object capable of vibrating has a natural frequency of 15vib/s. If at the beginning, with the system at rest, the object is set to vibrate at 25vib/s, it will soon vibrate at 25vib/s but with small displacement from the equilibrium position. This is because the system is trying to vibrate at its natural frequency. Suppose the driving force is gradually slowed down from 25vib/s to 15vib/s, the natural frequency of the system, so that the alternations of the driving force come just as the system is ready to receive them. When this happens, the amplitude of variation becomes very large, building up until the energy supplied by the driving force is just sufficient to overcome friction. Under these conditions, the system resonates with the driving force. A small driving force of proper frequency can build up very large amplitude of motion in a system capable of vibration. A motor running in the basement will often set certain pieces of furniture into vibration.

Resonant vibrations are a problem with heavy machinery. These equipment need to be stable but resonance could create vibrations that are too strong for the machine to withstand. This can be solved by changing the natural frequency of a part that is resonating. The extent of damage that resonance can do was illustrated by what happened to the Tacoma Narrows Bridge. This bridge was constructed in such a manner that the central span resonated until the resonance became so great that it eventually collapsed. However, resonance is not entirely hazardous. Its effect in violins and cellos create musical tones that are quite pleasing to the ears. Resonance is also implemented in radios. A radio station transmits a signal at a particular assigned frequency and any listener will just turn the dial on their radio to resonate his radios to the frequency of the station.

Posted 2011-01-29 and updated on Jun 08, 2011 12:24am by crisd