Nail

sink three nails in as few strikes as you can.

a hammer bobbing over a nail: tap to swing, and only a square hit drives it

The hammer comes straight down from wherever it is when you tap. High drives deep, low drives a little, and a face that lands a finger off the nail head folds the nail over. Harder wood sways the hammer further, so the square moment shrinks to the top of the swing.

Concepts: momentum, geometry, energy.

An interactive you play with one thumb, on Wundr.