Tacoma Narrows Bridge (1940) Billah and Scanlan (1991) reported that in fact, many physics textbooks (for example Resnick et al. and Tipler et al.) wrongly explain that the cause of the failure of the Tacoma Narrows bridge was externally forced mechanical resonance. Resonance is the tendency of a system to oscillate at larger amplitudes at certain frequencies, known as the system's natural frequencies. At these frequencies, even relatively small periodic driving forces can produce large amplitude vibrations, because the system stores energy. For example, a child using a swing realizes that if the pushes are properly timed, the swing can move with a very
Amplitude versus offset down the Zoeppritz equations. Due to its physical origin, AVO can also be known as amplitude versus angle (AVA), but AVO is the more commonly used term because the offset is what a geophysicist can vary in order to change the angle of incidence. (See diagram) For a seismic wave reflecting off an interface between two media at normal incidence, the expression for the reflection coefficient is relatively simple: where formula_2 and formula_3 are the acoustic impedances of the first and second medium, respectively. The situation becomes much more complicated in the case of non-normal incidence, due to mode conversion