The constructal-law origin of the wheel, size, and skeleton in animal design
This paper shows that the emergence of body organs is predictable as an integral part of the design for moving animal mass more easily on Earth, in accord with the constructal law of design in nature: For a finite-size open system to persist in time (to live), it must evolve such that it provides easier access to the imposed (global) currents that flow through it. Every organ destroys useful energy in two ways: Internally by thermodynamic irreversibilities and by having to be carried. From the constructal law follows the necessity of characteristic-size organs and the emergence of solid columns (legs) to facilitate the flow of stresses. This natural "wheel" endows the body with rolling (falling-forward) locomotion, with predicted speeds that agree with the observed speeds in the body mass range of 10-6-103 kg. The constructal law also accounts for animal design features for changing speeds. Skeletons (bones and legs) are solid organs that emerge in accordance with the constructal-law design of moving animal mass: More and stronger material emerges along the lines of highest stresses. A connection between animal wheel movement and swimming, water waves, and tsunamis is also made. © 2010 American Association of Physics Teachers.
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