Of Motion: Percussion, the Sling, and the Arm as Lever
Why the hand outruns the elbow, and why a rod struck at its middle is most powerful
Under the heading 'Of motion' Leonardo examines how throwing devices multiply speed. He observes that a rod or arrow struck at the middle of its travel receives a percussion of great power, and he diagrams a sling lettered b - a. He then explains why throwing-sticks hurl objects farther than the bare arm: in the same time the hand sweeps a far larger circle than the elbow, so it moves at twice the elbow's speed and drives thrown things farther, while the elbow covers half the distance and is half as slow.
On this page
A rod struck at the middle of its motion
Certain motions of movers receive their percussion in the middle of their movement, and these, Leonardo notes, are of great power. The point is illustrated by a rod with an arrow, struck at the middle.
The sling
A sling is drawn and lettered b - a, one of the throwing devices whose motion Leonardo is analyzing on this sheet.
Why the hand outruns the elbow (arm as lever)
Leonardo asks why throwing-sticks (lanciacampi) fling objects farther than the bare arm. Because in the same time the hand describes a far larger circle than the elbow, it covers twice the ground and so moves at double the elbow's velocity, driving thrown things farther, while the elbow makes half the journey and is half as slow.