On Motion: Percussion and the Persistence of a Blow
Three notes asking why a struck body keeps moving after its mover has left it
Three short paragraphs headed 'De moto' probe the mechanics of impact: whether a body driven by a single blow, without any lingering motion of the striker, would move only briefly, and why a struck body seems to wait for a thrust after receiving the percussion. A third note asks why a stone flung by a machine, having matched its mover's full power and speed at the outset, does not simply keep that same first motion instead of dividing from it and slowing. A small schematic sketch of a launching arm (a catapult) stands at the upper right beside the mirror-writing.
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A blow without lingering motion gives only brief travel
If a body moved by the blow of its mover took its motion from simple percussion alone, without any consequent motion of the striker itself, then the moving body would be of brief motion. Leonardo treats the persistence of a projectile as evidence that the mover keeps acting after contact.
Why the struck body waits for its thrust
If the act of percussion is the first power found among us, why does it not at once drive the moved body away, and why does that body then await the thrust after the percussion is received? He also asks why a machine-flung stone, matching its mover's full power and speed at first, does not keep that equality of motion without parting and slowing.
Schematic catapult sketch
A small line drawing of a launching arm sits at the upper right of the page, the material 'machine' whose flung stone the motion notes discuss.