Weight of a Body Turning on a Wheel or Rod about a Pole
How a load's effective gravity changes as it rotates about a central pivot
Leonardo studies how the effective weight (gravita) of a load changes as a rod or a wheel turns about a single pole or centre, marking the pivot 'polo' beside each diagram. He argues that a weight carried up or down through the rotation yields a 'variety of weight' at every degree of motion. But when the pole sits at the middle of the rod with an equal counterweight opposite, or when the load turns on a perpendicular pole, the weight neither grows nor diminishes; a longer pole suffers still less. The sketches show rods and wheels with balls at their ends, an arc of travel, and a disk mounted on a vertical shaft.
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A load turning about a single centre varies in weight
A weight fixed to a wheel or rod that must turn about one centre, so that it rises or falls, gives a different effective weight at every degree of its motion. The same holds when it turns about a single pole set along a horizontal (equidistant) line.
Balanced rod and perpendicular pole give no variation
If the pole is set at the middle of the rod and an equal weight is counterposed on the opposite side, no motion ever changes the weight. Likewise a weight at the rim of a wheel mounted on a perpendicular pole never gains or loses gravity through motion, and the longer the pole the less its effect.