Man-powered machines: force on an axle, a wing, a windlass
Three figures on how much force a man adds to a lifting device
Three large figures show men operating lifting mechanisms of beams, pulleys and drums, each accompanied by a note on the force involved. The first observes that a man, between his weight and his effort, presses on the axle where he sets his feet with more than the weight of three men. The second remarks that raising a wing costs less effort than lowering it, because the central weight to be brought down helps the lift; the third notes that turning a windlass with a worm screw makes the operator lose the weight he had been pressing with his feet, which he could regain by bracing his shoulders above.
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First figure: a man weighing on the axle as more than three men
Between his own weight and the force he exerts, the man presses on the axle where his feet rest with more than the weight of three men. The note quantifies how a treadle or footboard multiplies the load a single operator delivers to the mechanism.
Second figure: raising a wing costs less than lowering it
It takes less effort to raise the wing than to lower it, because in raising it the weight in the middle that one wishes to bring down helps a great deal. The remark concerns the balance of forces in beating a large wing-like arm.
Third figure: a windlass with a worm screw
Turning the windlass, the operator loses the pressing he was doing with his feet; he would regain it if he could brace with his shoulders above. The figure is labelled with a worm screw (chiocciola vite) driving a drum.