On weight, equilibrium, and the nature of the lever
Balancing a body on one point; 10 pounds at the end equals 40 at the quarter
Turning from percussion to statics, Leonardo studies weight, balance, and the lever. He shows how a body of any strange shape can be made to rest on a single point by adding a counterweight (labeled c b) so that the support a falls at the true center of weight. A bent rod (a m b) wedged between floor and beam illustrates how a compressed piece straightens with force enough to make floor and walls tremble, and a lever diagram states the rule that 10 pounds at the end does as much as 20 at the middle and 40 at the quarter. A final balance (10, 10, a) asks which of two equal weights will do more harm to a hand placed at a.
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Balancing a body of any shape on one support (c, a, b)
A weight supported in the middle, whatever its strange form, steadies itself in equilibrium on its support. Let a b be a piece of ruler resting only on end a: it can hold only if you add the weight c b as a counterweight, so that a lies in the middle between c and b and rests on the pole a.
A rod bent by force within a frame (a m b)
Every bent body decreases its length, and once bent it straightens with force, thrusting aside any heavy obstacle. Wedge a rod between the floor and the beam above so that an 8-braccia rod has two fingers of bend; shake it along its bend, and the whole floor and walls tremble.
The nature of the lever: 10, 20, 40
On the nature of the lever: ten pounds at the end of a lever does as much as twenty at the middle, and as much as forty at the quarter.
Which weight harms the hand at a?
On a long rod in balance carrying two equal ten-pound weights, Leonardo asks which of the two will do greater harm to the hand placed at a.