Equilibrium of Balances and Systems of Pulleys
Statics of the weighed beam, and the ratio of motion to load in pulley tackle
A sheet of statics in which Leonardo sets down rules of equilibrium: an infinitesimal 'excess' of weight is enough to tip two equal pans, and a load descends less the stronger the support beneath it. A central diagram of a hanging balance, lettered with angles, tests whether the ratio of the arms g b to g n equals the ratio of weights 1 and 7, while Leonardo cautions that experience does not yet confirm the rule. Below, a row of pulley and windlass diagrams explores how a load is divided among several cords, so that the motion of a lighter branch is proportionally longer than that of a heavier one.
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The 'excess' weight and rules of equilibrium
A single quantity of excess suffices in nature to tip one of two equal pans, making that weight always victor over the other; among bodies this excess is as the point on a surface. A weight descends less the stronger the support that holds it, and the part of a support farther from its fixing-point resists least.
Testing the arm-ratio of a lettered balance
The hanging balance is lettered so that a and b are kept as right angles. Leonardo proposes that the ratio of g b to g n equals that of weight 1 to weight 7, but warns that here experience does not confirm it and that one must experiment before setting down such a rule as general.
A load divided among many cords
The lower diagrams show pulley tackle in which a weight is shared out among several ropes; in one system a weight is divided among eight cords, the ninth alone sustaining only what the eighth passes to it. In another group of four pulleys, a branch feeling half the weight travels correspondingly farther.
Motion inversely proportional to weight
Across the pulley studies Leonardo states the proportion generally: the ratio of motion b to motion a is the same as that of weight a to weight b, so the powers and the motions they produce stand in one and the same proportion.
