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# Physics/Atwood Machine

Question
QUESTION: I was wondering if the human back is an atwood machine with the spine providing nerve conduction and flexibility to the core. Can the legs be our two hanging masses which rest with the downward force of gravity at standing but have an impact force on walking? Hip is our pulley lifting and lowering weight at spinal regulation?

Not an anatomy major but this sounds like a reasonable model.

ANSWER: No, Atwood's machine is very specific.  It is a pulley with weights on either end, pretty dissimilar in almost every respect to the human back.  The hips are more of a tilting platform.  I can see where you're going with trying this as a model, but humans are not magically supported in space by their spine with hanging legs.  Human legs do the actual supporting while we walk, and are a complex double pendulum with a non-simple bob at the end.

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QUESTION: Okay - what would the physical model of walking look like. I am a maths major having mental picture issues on this stuff. I am fine in isolation but when I try to go from a part to a whole my mind breaks it down in a screwball fashion. If it helps I am a maths major with a focus in analysis and my second major is computer science with a focus in security.

A physical model of walking must take into account all stages of the gait.  That's really complex.  See here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2816028/  Scientists have been studying human gait for decades, it's still an active area of research.  The models are too complex to form in your mind, they have to be considered on a piece-by-piece basis, as with all projects of such complexity.  Generally, walking resembles a coupled set of pendulums, joined by a torsion spring (the torso to shoulders/hips) or joints (knees, elbows connecting two pendula directly).  They also have to account for the fact the elbows and knees have limits to the direction they can flex.  This analysis may be of further help: https://staff.fnwi.uva.nl/a.j.p.heck/research/walking/walking.pdf

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