Percussion, colliding balls, and the force of the crossbow
A blow is motion stopped by resistance; how deep a weight sinks when dropped
Continuing the science of percussion, Leonardo defines a blow as 'motion interrupted by a resisting object': there can be motion without a blow, but never a blow without motion. He compares the thunder of a bombard to lightning (fire struck in the air) and poses two proportion problems on how deeply a falling weight sinks into the ground. He observes that a body drawn far beyond its nature returns with greater force, as in the crossbow, and that two equal balls thrown against each other stop dead, each undone in the other. A small diagram of colliding spheres illustrates how their courses exchange, and he notes how a blow struck above or below the crossbow's cord behaves differently.
On this page
A blow is motion interrupted by resistance
A blow is motion interrupted by a resisting object; there may be motion without a blow, but never a blow without motion. A sharper piece of metal driven against a blunter one buries itself in it, and a ball of fresh earth thrown back into its mass keeps part of its round form.
How deep does a falling weight sink?
If a weight of a hundred pounds, dropped ten times from ten braccia onto one spot, sinks one braccio, how far will it sink falling from a hundred braccia? A parallel problem asks how far a hundred-pound weight sinks where a ten-pound weight sank half a braccio.
The crossbow returns force drawn beyond its nature
A body drawn further beyond its nature returns with greater impetus once it is free, and this is the crossbow. That blow is greatest whose struck point, striking weight, and starting point lie on one straight line.
Two colliding spheres exchange their courses
If two balls are thrown upward so that they collide, the course of the right one transfers into that of the left, and the left into the right. Two equal balls thrown in a straight line against each other stop dead, each undone in the other.