On Motion: Why the Bombard Alone Increases Its Force
The longer a ball travels in the barrel, the more powder ignites and the harder it is driven
Four notes headed 'De moto' continue the study of impelled motion: the longer a mover accompanies a body, the farther it carries it, yet almost every cause of motion loses power before it parts from what it moved. Against this, Leonardo argues that the bombard is unique in increasing force, because over the ball's longer travel inside the barrel more powder catches fire in divisible time, pressing harder and hurling the ball out with greater fury. A final note poses the open question of whether a mover carries a body farther by starting slow and gaining impetus or by starting fast and slowing.
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Movers spend their power before parting from the body
The more a moving power accompanies a body, the farther it removes it from the point of parting; yet almost universally, whatever causes motion diminishes its power before it separates from the thing it moved. These two notes frame the general rule against which the bombard is the exception.
The bombard increases force as more powder ignites
The bombard alone increases its force, because over the longer travel the ball makes within the barrel, more powder is ignited; the catching of fire happens in divisible time, so the longer it lasts the more powder burns, the more the fire is pressed within the instrument, and with greater impetus and fury it drives the ball out.
Slow-then-fast or fast-then-slow?
A closing question asks, over the same travel of the mover, whether it removes a body farther by beginning with slow motion and always increasing the impetus, or by beginning fast and going on slowing.