A pendulum, pushed on a schedule. Off its natural rhythm it barely stirs; drive it at the one frequency it was born holding and every stroke lands in step, so the swing climbs far past the hand that feeds it — a held tone shattering a glass, a column walking a bridge down.
Drag across the stage to sweep the push. The curve is the pendulum's whole appetite; sharpness Q makes it narrower and slower to build. Tap sounds the response — loud at the note, near-silent off it.
off the note — the push is wasted.