Claw

slide the claw over a prize and let go.

an arcade claw machine: slide the claw, drop it, and a prize gripped off its middle tips and slips out

The claw is weak on purpose: it holds a prize only while the prize hangs straight under it. Grab one by its middle and it lifts level; grab it by the shoulder and it turns until its weight is under the prongs, and if it turns too far it slides out. Bigger, softer prizes forgive more; the small heavy ones forgive almost nothing.

Concepts: torque, pendulum, balance.

An interactive you play with one thumb, on Wundr.