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Paris Manuscript L — 92

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Bibliothèque de l'Institut de France, Paris

Quanto la ballotta sarà più polita, tanto fia più facile a girarsi per l'aria onde si move.

In questo modo del proporre1 s'immagina che la pallotta mossa dalla bombarda abbia a girarsi nell'aria da lei condensata, la quale essendo essa ballotta mal pulita, essa abbi difficile confregazione curva coll'aria che la veste, come provai nel quarto delle confregazioni.

Adunque il balzo di tale ballotta, quando risalterà con angolo più ottuso, essa ballotta più girerà in sé e se essa balla sarà mal pulita, ella verrà a mancare di sua velocità assai più che se essa fussi pulita.

The more polished the ball is, the more easily it turns through the air in which it moves.

In this way of framing the matter, one imagines that the ball shot from the bombard must turn in the air condensed by it; and that ball, being badly polished, has difficult curved friction with the air that clothes it, as I proved in the fourth book of frictions.

Therefore the bounce of such a ball, when it rebounds at a more obtuse angle, causes the ball to spin more upon itself; and if the ball is badly polished it will come to lose much more of its velocity than if it were polished.

Why a Polished Cannon-Ball Flies Truer

Surface friction, spin and loss of velocity in a ball shot from a bombard

Physics & Mechanics Weapons & Fortification

A page of continuous text argues that the more polished a ball is, the more easily it turns through the air it moves in. Leonardo imagines a ball fired from a bombard spinning within the air it has condensed; a poorly finished ball has 'difficult curved friction' with that air, a point he says he proved in his fourth book of frictions. He concludes that when such a ball rebounds at a more obtuse angle it spins more upon itself, and that a rough ball loses far more of its speed than a smooth one would.

On this page

A rough ball loses velocity through friction with the air

A polished ball turns more easily through the air; a badly finished one meets 'difficult curved friction' with the air that clothes it. When the ball rebounds at a more obtuse angle it spins more upon itself, and a rough ball therefore loses much more of its velocity than a smooth one, as Leonardo says he proved in his fourth book of frictions.

Reader's Edition — described with AI from the e-Leo transcription.