Cords of a tackle-block: which rope breaks, and the reflection of wind
Load shared among pulley ropes, breaking toward the mover, and reflected air
On this verso (100v) Leonardo continues the science of ropes as applied to tackle-blocks (taglie), a compound pulley of which is drawn in the center with several sheaves. He argues that cords of uniform strength share the load equally, that no single rope of the tackle breaks without all breaking, and that the part joined to the mover always feels the greater weight, since the mover must exceed the load for motion to occur. Lettered figures fix the breaking points (a b, n a, n q f a r) at the highest, most loaded parts of the run. A separate top-right note records an experiment blowing air from a bellows onto a board (b c), finding that reflected motion is not made at angles equal to the incident motion.
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Uniform tackle ropes share the load and break toward the mover
All the cords of a tackle-block of uniform power sustain an equal part of the applied weight, and no one rope breaks without all breaking over the axle. The cord that descends to the hands of the mover breaks where it leaves its pulley, because in moving the mover is more powerful than the load. Thus the cord a b feels more weight than the cord n a, and a b weighs more than a n.
The part joined to the mover always feels the greater weight
The part of the cord joined with the mover always feels greater weight than the part joined with the load, for if the mover were not more powerful than the load no motion could be given. The cord between the pulley and the mover overcomes both the friction of the axle and the weight. Toward the mover the ropes carry both their own weight and that of the mover, which prevails.
Compound pulley (tackle-block) with lettered breaking points
A tall compound pulley with several stacked sheaves is drawn in the center, with a weight hanging at its foot. Leonardo predicts that the cord a n r will break at n, and that if the little windlass were placed at f the cord would break at point q, as the heavier part. He adds that a cord of uniform power always breaks at its highest point, its attachment.
Wind reflected off a board is not at equal angles
In a top-right note with a triangular figure (a, e, b, c, f), Leonardo reports blowing air from a bellows a onto the board b c. He finds that the reflected motion is not made at angles equal to its incident motion, since the wind flees toward c f as toward b e. The observation belongs to his study of the behaviour of moving air.