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 distortion more than two waves as well. In a narrowband system such as a radio communication system, unwanted outputs such as X-Y and 2X+Y will be remote from the wanted band and so be ignored by the system. In contrast, 2X-Y and 2Y-X will be close to the wanted signals. These so-called third order distortion products (third order as m+n = 3) tend to dominante the non-linear distortion of narrowband systems. Amplitude distortion is measured with the system operating under steady-state conditions with a sinusoidal input signal. When other frequencies are present, the term ""amplitude"" refers to that of the fundamental