planemad_bk:
Did you ever see the movies of "galloping gertie", the suspension bridge at Tacoma WA. that oscillated so badly that it collapsed? (1940)
A Crankshaft is similar in that it is subject to vibratory excitation in what is called a "spring-mass system". When in resonance, it can break - the same way a soprano can shatter a wineglass with her voice.