Impact of Balls, a Water Splash and the Wearing of an Axle
Collision of two equal balls along the line of their centers; a stone striking water; how a wheel's axle wears its support
The upper diagrams treat two problems in motion: a ball b travelling along line n d strikes an equal ball at a, and after impact both move along line o r joining their centers through the point of percussion; and a stone dropped vertically onto water makes the water rise back up along a perpendicular line. The lower half studies a loaded wheel on its axle, arguing that the axle wears away its support along an oblique line running from the middle of the cord's contact to the axle's center, and that it wears toward the winning power, since n overpowers weight a and the turning axle strains toward the force that draws it. Lettered figures (c d f, a o, b r, n; t n, S, m) key the geometry.
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Rebound of two equal balls after impact
A ball b moving along line n d meets on the way a ball at a, equal to b in weight and shape. Leonardo says the motions that follow the percussion run along the line found between the centers of each ball and the point of their percussion, that is the line o r.
Water rising vertically where a stone strikes
If a stone is let fall from high to low upon water along a perpendicular line, the water lifts from the struck place and rises likewise along a perpendicular line. The upper-left figure shows the jet springing up above the point of impact.
A wheel's axle wears its support along an oblique line
The axle (polo) of any wheel wears away its support along an oblique line, which runs between the middle of the cord's contact on the wheel and the center of the axle, as shown by line t s. The lower wheel diagrams illustrate the loaded axle and its cord.
The axle wears toward the winning power
The support of the axle is worn toward the near cause of its motion: because n moves weight a by force, n's power surpasses a's, and the surpassed obeys. The turning axle desires to travel toward the winning power and, being held back, wears away its support over time.