How weights press, and the advantage of machines
The four passions ranked; how a weight's shape governs its pressure; and why force extended through wheels, levers and screws grows.
Leonardo returns to weight, force, motion and blow, describing how weight presses eternally through its supports down to the center of the world, and ranking the four 'passions' by permanence and power: weight least powerful but most lasting, the blow most powerful but shortest-lived, motion the child of force and the blow the grandchild. A row of small diagrams (a bar and a circle, a square and an oblong, a triangle and a rectangle, a tapering stack of blocks) tests how a weight's shape and proportions affect how hard it presses or how deeply it penetrates its support. A closing note on the arrangement of force explains that extending it from wheel to wheel, lever to lever or screw to screw makes it more powerful but slower, and that the force taking longer is the stronger.
On this page
The four passions ranked by power and permanence
Weight presses eternally through its supports to the center of the world and is least in power though most lasting. Force is more powerful but less lasting, motion more powerful still and born of force, and the blow the most powerful but shortest-lived, child of motion and grandchild of force. All are born from weight.
Two weights of equal contact press equally
If two equal weights, one round and one long, each touch the ground as much as the other, then each will press as much as the other.
A taller weight presses twice as much
Of two equal weights of the same width but one twice the height of the other, the taller will press twice as much on its support as the shorter.
Equal base and weight press equally despite shape
If weights are equal in base and weight, then even with different proportions they will press equally.
How proportion governs pressing and penetration
A weight whose height fits several times into its width pushes and presses less against the ground; a weight whose width fits several times into its height penetrates the ground more than any other.
Extending force through wheels, levers and screws
The more a force extends itself from wheel to wheel, lever to lever, or screw to screw, the more powerful and slow it becomes. Of forces from a given motion, the one consuming more time is the more powerful, weaker in proportion as its time enters into the other's.