Against perpetual motion, balances, and the fall of bodies
Weights on balances, resonance of bells and lute strings, and how spheres fall by diameter
The page opens with Leonardo's argument against perpetual motion: nothing inert moves of itself, and once the first mover's impulse ceases the motion stops. Diagrams of suspended rod balances and an experimental pulley system illustrate how a lighter weight can raise a heavier one only by moving farther and faster. Further notes on "the blow" describe how a struck bell impresses its "likeness" and sets a like bell or lute string resonating, while closing propositions relate the speed of falling spheres to their diameters and the accumulation of weight to the speed of descent.
On this page
Against perpetual motion
No inert thing moves by itself; when it moves it is moved by an unequal power, whether of unequal time, movement, or weight. And once the desire of the first motor ceases, the second immediately ceases.
Balances and mechanical advantage of weights
On equal-armed balances, weight b must be heavier than a to lift it. For d to lift the heavier c, d must fall through a greater course than c rises, so its balance-arm must be longer; and for the small weight f to lift the large weight e, f must move farther and more quickly than e. The weights a, b, c, d, e and f are shown on suspended balances and a pulley system.
Resonance of bells and lute strings
A blow given to a bell causes a similar bell to respond and move somewhat; likewise a plucked lute string sets another string of like voice sounding in a second lute. This can be seen by laying a piece of straw over the string similar to the one played.
Falling spheres and their diameters
If two spherical bodies of the same material fall at the same time from the same height, the one falls as many times faster than the other as its diameter enters into that of the other. Leonardo restates the proposition for two unequal weighty spheres of equal material dropped from a height.
Accumulated weight and speed of descent
If one pound falls on one pound of resistance it does not change but remains equal; add another pound and it descends to earth in a certain time; add yet another and the whole weight descends at twice the speed.