The law of the balance and motion on wheels and rollers
Weights in inverse proportion to their arms; ease of rolling versus support on the axle
On folio 178r the balance is stated as a proportion: weights that resist one another on the beam stand in the same ratio as the opposite spaces interposed between their perpendiculars and the fulcrum. Further rules note that straight sides of bodies curve under weight, blow or force, and that a beaten cube grows rounder. Two rules on motion hold that a load rests-and-moves more easily upon rollers, wheels or balls than when carried on their axles, and that the greater the difference between wheel and axle diameter, the easier the motion. Marginal diagrams show hanging-weight balances (numbered 59-63) and a wheeled cart, with a note that point a has no axle-contact with the load while b does.
On this page
The balance: weights inverse to their arm-spaces
Weights that resist one another on the balance have the same proportion among themselves as the opposite spaces interposed between the perpendiculars of the weights and the pole (fulcrum). The hanging-weight beams sketched at the upper left set out the geometry.
Bodies deform, and cubes round, under blow and force
The straight sides of bodies become curved if they are pressed by weight, blow or force; and the more a square cube of equal angles and sides is widened by the blow, the rounder its figure becomes.
Rolling is easier than support on the axle
A weight resting on rollers, wheels or balls is moved more easily than one supported on their poles (axles); and the greater the difference between the diameter of the wheel and that of the axle, the easier the motion found in it. The wheeled cart at the lower left illustrates the case where point a lacks axle-contact and b has it.
Contact of pole with the load
A caption beside the lower-left cart notes that a has no contact of the pole (axle) with the weight, and b does. The labels a and b mark the two rollers under the load.