Blow and Force as accidental weight
The crossbow's force in the arrow, heating by friction, and a man lifting his own weight by pulley
Leonardo defines both blow and force as 'accidental weight' applied by motion to natural weight, the blow being the more powerful the briefer its action. He argues that the natural weight loading a crossbow is transferred as accidental weight into the arrow it shoots, that a body rubbing swiftly on another heats up while one flying through the air is chilled, and that a red-hot iron cooled in water warms the water proportionally less. A small sketch at lower right shows a man raising a load with a pulley fixed above him, lettered a (the man) and b (the weight).
On this page
Blow and force defined as accidental weight
Blow and force are accidental weight applied by motion to natural weight. The blow is of greater power than force by as much as its action is briefer, even when the two are created by equal power.
The crossbow transfers its loading weight to the arrow
As much natural weight as loads the crossbow through its free descent, so much accidental weight is infused into the arrow shot from that crossbow.
Friction heats, flight chills; cooling hot iron in water
A dense body driving fast through the air is penetrated by greater cold, while one rubbing swiftly on another dense body heats up. If a red-hot iron is cooled by water, the water's gained heat is weaker than the iron's was, in proportion as the water exceeded the iron in quantity.
A man lifting a weight with a pulley (a the man, b the weight)
A man with a pulley fixed above himself, pulling by simple traction, can never without a jerk raise a weight equal to that of his own body. In the figure a is the man and b is the weight.