Why a hammer-blow fails to drive an iron peg from wood
Percussion study: the iron a b bends before the blow at b can dislodge the peg c from wood m
The upper diagram shows a hammer poised to strike a horizontal iron (labelled c a b) set into a block of wood m. Leonardo argues the blow is not effective to dislodge the iron: striking at b, the arm a b first bends and makes force at c, and because b rests on air the blow is not received with the hammer's full descending power, so no thickness of iron makes the blow effective. Further untranscribed sketches, including a T-handled tool, a faint spiral, and a small four-wheeled wagon, also appear on the sheet.
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The ineffective blow on iron c in wood m
When the hammer strikes at b, the iron a b first bends, making force at c, and b, resting on air, does not receive the hammer's full descending power. Hence the blow can never dislodge the iron, whatever its thickness.