Balance of Two Poles; Weights, Cords and Cord-Strength
The statics of suspended loads and the breaking of cords, with a domestic memorandum
The reverse of the beam studies, opening with a 'balance of two poles' and red-ink sketches of weights carried by cords over pulleys. Leonardo argues that the true counterweight of a simple rod lies at its midpoint, that a weight is most weakly held the farther it sits from the fastening of the crossbeam, and that a cord of uniform strength breaks where it bears the greatest load, including its own weight. He closes with the principle that heavy bodies naturally seek to make their centre the centre of all the elements. A stray marginal note—'Boil eggs and dried food'—records a domestic errand amid the mechanics.
On this page
The balance of two poles
A heading naming the apparatus studied on the sheet: a balance suspended from two poles, developed through the figures of weights hung on cords.
Where a load is most weakly supported on a crossbeam
The true counterweight of any simple rod lies at the middle of its length. A weight is the more weakly supported the farther it sits from the fastening of one end of its crosswise support, since that part of the support resists least.
A cord breaks where it bears the most load
A cord of uniform strength could be imagined so long that its own weight would break it. Overcome by excess weight it snaps where the load is greatest—the part that carries both its own remainder and the suspended weight.
Heavy bodies desire the centre of the elements
The natural motion of heavy things reveals their own desire: every heavy body wishes its centre to become the centre of all the elements. The heavier part becomes the head and guide of the movement.
Weights carried over pulleys
Figures of weights supported by cords running over pulleys, labelled with the numbers 44; 44; 4; 16 8 4, showing how a load is divided among the cord runs.
A domestic memorandum
In the right margin, unrelated to the mechanics, Leonardo has jotted a household reminder to boil eggs and buy dried food.