The Arrow and the Bowstring; Rebound Angles and the Oblique Body
A thrown body never outruns its instrument; rebound angles mirror the line of percussion
Propositions comparing motion by an instrument with motion by a blow, illustrated by lever and arc-shaped devices (numbered 15, 16, 17) and a round body drawn as a circle with center lines. Leonardo reasons that a body thrown by an instrument never moves as fast as the instrument itself — otherwise the arrow would leave the bowstring before the string finished its course — and that a body thrown by a blow travels faster than one merely pushed. He adds that the angle of rebound mirrors the line of percussion, that a round body on an oblique support loads it with twice the weight of the part above its central line of contact, and that a blow struck at more unequal angles is weaker than its impetus warrants.
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A thrown body never outruns its instrument
The flight of any body thrown by the motion of an instrument is never as fast as the thing that throws it; otherwise the arrow would leave the bowstring before the string completed its course. The flight of a body thrown by a blow is much faster than one pushed by motion.
The rebound angle mirrors the line of percussion
The angle of the rebound of struck bodies is similar to that of the line of percussion. A blow struck at more unequal angles is much less powerful than its impetus and weight would warrant.
A round body on an oblique support
A round body placed on an oblique location gives its support twice as much weight as the part of it found between the central line of contact and the upper part of the oblique location.
Arc lever and pivoted-arm devices (15, 16, 17)
Small mechanical sketches accompany the text: an arc-shaped arm on vertical posts, a horizontal bar with a ball at each end, and a T-shaped pivoted lever, numbered 15, 16, and 17. They illustrate the throwing and rebound cases discussed.