Cart wheels and the ease of hauling
How unequal front and rear wheel heights change the effort of motion
A cart is drawn schematically as two wheels on a common ground line, their centres labelled t and S (A). Leonardo reasons that with wheels of equal height the cart moves with a fixed force, but raising the two rear wheels makes it move more easily, while lowering the front wheels makes the motion harder and more laborious. He fixes the geometry with the letters a, t, S and n: a t marks the centres of equal wheels, S t the centres when the rear ones are enlarged, and a n the centres when the front ones are lowered.
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Wheel height and the effort of hauling
With equal wheels the cart moves with a certain force; enlarging the two rear wheels eases the motion, while lowering the front wheels makes it more laborious. Let a t be the centres of the equal wheels, S t the centres with enlarged rear wheels (easy motion), and a n the centres when the front wheels are lowered; the difference in effort grows as the larger wheel exceeds and the smaller falls short of the original.
