Resonance

The tendency of a system to oscillate with greater amplitude at some frequencies then others is called resonance. Resonance comes form the latin word for "resound". Frequencies at which the response amplitude is a relative maximum is known as the resonance frequencies. at these resonant frequencies, it is possible for even a small periodic driving force can produce large amplitude oscillations because the system tends to store vibrational energy. Resonance occurs when a system is able to store and easily transfer energy between two or more different storage modes. A resonant frequency of vibration is determined by the physical parameter of the vibrating object. It is easy to get an object to vibrate at its resonant frequencies and hard to get it to vibrate at other frequencies. A vibrating object will pick out its resonant frequencies from a complex excitation and vibrate at those frequencies, essentially, filtering out other frequencies in the excitation. Most vibrating objects have multiple resonant frequencies.
In music, there is a mathematical relationship between the standing wave concept and the musical instrument, mathematical relationship between the frequencies and the sound the instrument produces. The sound produced by an instrument is caused by resonance. Musical instruments are set into vibration motion at there natural frequency when a person disturbs the instrument. each natural frequency of the object is associated with one of the many standing wave patterns by which that object could vibrate. The natural frequencies of a musical instrument are sometimes referred to as the harmonics of the instrument.
Examples of resonance gone wrong, On the morning of November 7, 1940, the four month old Tacoma Narrows Bridge began to oscillate dangerously up and down. A reporter drove out on the bridge with his cocker spaniel in the car. The bridge was heaving so violently that he had to abandon his car and crawl back to safety on his hands and knees.
At about 11:00 the bridge tore itself apart and collapsed. It had been designed for winds of 120 mph and yet a wind of only 42 mph caused it to collapse. How could this happen? No one knows exactly why. However, the experts do agree that somehow the wind caused the bridge to resonate. It was a shocking calamity although the only loss of life was the cocker spaniel.
Nikola Tesla was a genius obsessed with resonance. He had attached a small vibrator to an iron column. At certain frequencies specific pieces of equipment would jiggle, change frequencies and the jiggle would move to another part of the room. He had not accounted for the column that ran down into the foundation, he was transmitting frequencies all over manhattan.
Tesla was using the vibration of resonance to create a small earthquake, smashing windows and swaying buildings.
The schumann resonances are a set of spectrum peaks in the extremely low frequency (ELF) portion of the earths electromagnetic field spectrum. schumanne resonances, excited by lightning discharges in the cavity formed by the earths surface and the ionosphere.