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مردم (انسان ) ماده و محیط MAN – METERIAL – MIDDEN ( ENVIRONMENT) | ||
| نشریه دانشکده فنی | ||
| مقاله 18، دوره 20، شماره 0 - شماره پیاپی 1000200، مهر 1350 اصل مقاله (200.09 K) | ||
| نویسندگان | ||
| پرفسور اتمر؛ هرمز پازوش* | ||
| عنوان مقاله [English] | ||
| Man- Materials Midden ( Environment) | ||
| چکیده [English] | ||
| The conjunction of millions of coincidences over millions of years with the almost infinite odds of their all fitting together in the appointed sequence has brought forth living organisms, plants, animals, and man! These happenstances have resulted in building up to an apex of biologe-people-you and me! This earth may well be unique in time or space, limitless as re both. Where these mathematical odds have been upset, life has developed and evolved into reasoning, motivated beings which have benn able to control and use for their own purposes all other forms 'Of life and materials. Recently, Went, in The American Scientist, in a fascinating evaluation of man's dominance. demonstrated that man's physical size has evolved from natural laws to an optimum under earth's conditions. His arguments are intriguing and convincing. Going back to axioms: - there are two types of properties - mechanical and molecular. Reynolds' Criterion shows that when mechanical properties of fluids -control fluid flows according to one law, when, molecular properties control the flow is quite different. A similar critical condition also based on dimernions -fixes controls for many other phenomena of matter and even of the living of animals, since mechanical forces of mass, inertia. etc. exert their effects to a quite different extent than mole- cular properties, as diffusion, viscosity, cohesion or attraction and visecosity. Weight increases with the third power of length, while the molecular forces attracting bodies in contact with each other increase approximatelyl as only the first power. A 1ammo cube with a flat side might be just supported by adhering to another flar surface; molecular forces of attraction just balance mechanical forces ofseparation . If larger' the cube falls; and if the cube has edges 10 times as long, gravity is 50 times as strong. while if the edges are onetenth as long, adhesioe is 50 times as strong. The criterion of the control by molecular forces or by mechanical forces for many other phenomena are similar and as important as in Hydraulics. Criteria like Reynolds' need to be considered in many fields. This can be appreciated qualitively; e. g. dust particles stiak to walls and ceilings, even though they have weight. This mechanical force of gravity is very small compared to the molecular force of adhe , sion, which is overcome only by a much more powerful mechanical force, that of a vacuum c1ener. Also, a small fly can walk on the ceiling; its force of adhesion is greater than its weight. Very large flies cannot; their size on the other side of the critical. Of more interest is a similar criterion for the method of distribution of oxygen. water. and food in a living organism. Single cells distribute food by molecular diffusion. This is extremely fast in single cells which, for example, complete by diffusion all the functions of a generation of life in 20 minutes. Insects, as ants, are at akout the critical size: and all mass transport inside their bodies is by diffusion. Man's size at 10 to 50 million times the ant's is far above the critical: and diffusion would take a lifetime bring sustenance from his stomach to his feet and hands. and would energize only a few steps in his lifetime. Animals above the critical size have developed many and ingenious pumps for gas and liquids. to distribute mechanically the fluids which support life. Went carries this idea further into the mechanical domain. showing why a small animal could not use fire - the flame of which has a critical size, could not have an information storage system which would allow the development and inheritance of a culture. could develop too little energy to utilize tools or weapons effectively, would have too small a nunber of brain cells: while an animal much larger than a man | ||
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