Of Tackles: Where a Loaded Rope Breaks
A rope of uniform strength snaps where it bears the most of its own weight
Opening a section "of tackles," Leonardo takes up where a rope of uniform strength will break under load. Using a suspended rope a b able to resist a thousand pounds, he argues that if it weighs a thousand and one pounds it breaks near the top a, where the greatest length of rope hangs below and the strength is at its last limit. Marginal sketches show a rope wound on crank-driven rods and passed over pulleys, with a movable weight n, and a crossbow whose string illustrates the same principle. He notes that a rope set in different positions breaks in different places, and that a straight bow breaks its string at the top where its straightness ends.
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A hanging rope breaks nearest the top, where its weight is greatest
Let rope a b hang from its upper end a and be able to resist a thousand pounds. If it weighs a thousand and one pounds it breaks nearest a, where the length weighing a thousand pounds ends, rather than lower where it weighs nine hundred ninety-nine, for there only one pound of strength remains and any added weight snaps it at once.
Rope wound on crank rods and pulleys, with a movable weight n
The right margin shows a rope wound on two crank-turned rods and passed over two pulleys. The weight n can be set at various points of the rope and pulled in various directions, letting the same breaking law be tested for different positions.
The crossbow string as proof of where a rope breaks
See where the crossbow breaks its string, and you will understand where this rope will break when overcome by force. If the bow is set straight, the string breaks in its upper part where its straightness ends, because the string's strength is whole in every part but to it is added the string's own weight.