Motors that gain or lose power, and pulley tackle
The science of motive power, with numbered pulley trains for studying friction
A densely worked sheet on the science of 'motors' (sources of motive power) and on rope-and-pulley tackle. In the side columns Leonardo classifies motors by whether they build up or spend power through their stroke, the bombard gaining force toward its end and the bow spending it, and proposes to measure a motor's power by the distance it drives a body in equal time. The central column sets out numbered pulley trains for studying friction, together with rules that a rope keeps its central length through any bend and regains its power at every support. Further mechanical sketches, including a hatched cylindrical device at the upper right, fill the margins.
On this page
Motors that gain or lose power over their stroke
Leonardo distinguishes motors that build up power toward the end of their action, like the bombard, from those that spend it, like the bow. He imagines one motor beginning at a power of a hundred and ending at one, and another beginning at one and ending at a hundred, each averaging fifty at its mid-point. He then asks which of the two would drive its projectile the farther, all else being equal.
Pulley trains numbered for friction
The central column sets out a series of pulley arrangements labelled with numeric loads (2, 4, 1 1/2, and so on) to study how friction alters the mechanical advantage. The figures track how the load carried changes as the rope passes over more sheaves.
A rope regains its power at every support
Leonardo states that a rope recovers its power as many times as it finds a support, each pulley or fixed anchor renewing the mechanical advantage of the tackle. The note accompanies a sketched system of pulleys marked with the figure 70.
How bending and stretching affect a loaded rope
The central line of a rope, Leonardo argues, never changes its length no matter how the rope is bent. The part of the rope that lengthens most under a bend is the part most burdened by the weight loading the whole.
Measuring a motor's power by the distance it moves a body
In the left column Leonardo proposes to measure the differences in power among motors by the differences in the lengths of the motions they impart in equal time. The variety in how far the moving bodies travel, driven with equal time and motion by their motor, gives the measure of the variety in their powers.