day 10: mobility

“A structure’s mobility is the amount it vibrates when driven by a fluctuating force.” –Stephen A. Hambric


KStar’s mobility is continually on my mind. (If only I could put it into my body so painlessly.)  It’s driven me to earn a degree in medicine, to develop a practice in orthopedic surgery, to work toward becoming a competitive CrossFit athlete and Olympic weightlifter, and to carry a lacrosse ball on my person at all times.  The mobility discussed by structural acousticians is not the mobility I care to study.


My task: explain, in layman’s terms, the transmittal of structural vibrations through a surrounding medium, focusing specifically on the mechanism for the resulting far-field acoustic radiation pattern.  This is a well-studied problem, so papers exist which lead me through the differential equations and transforms that explain the physics of propagation.  To complete my task it seems essential I explain why the structure vibrates as it does at a given frequency for a particular force; this is the first link between the structural vibration to the near-field radiation.  But nobody explains it! Instead they say “and we call this mobility.” I know, I know, its vibration is a certain amplitude for a given force because of the atoms and their crystalline/non-crystalline structure and the conditions of the environment and so on and so forth but settling on defining something that can be derived seems a bit incomplete.  Shamefully, I suspect my bitterness derives less from principle than from the thought of the work I need to do.  Oh, if I could use equations, this would all fit on one little line.  Math is lovely because it forces brevity, which I clearly lack.


Math, like one of KStar’s elastic bands, is a distractor.  Both allow me to do fantastical things, such as being brief or squatting with my knees out.  Yayyy math! Yayyy bands!


Also, I just got a paper cut.  CrossFit, Oly and mobility WOD are critical dampers to the simple harmonic motion of my wimpiness, but Jesus Christ this cut is throbbing.


Whoa–reallllll classy, KT. JC was crucified and you’re calling on Him for a paper cut.  


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