Knocking

Knocking is the act of striking a solid surface with a part of the body or an object to produce a sharp, brief sound. It is often performed with the knuckles, a fist, or a small tool, and most commonly serves as a signal to gain attention or request entry. The sound and rhythm of a knock can convey urgency, politeness, or warning, and the exact effect depends on the material struck and the force used.

Doors are the most familiar target, but knocks can occur on walls, tables, windows, or other hard surfaces. In everyday use, variations in tempo, loudness, and repetition communicate different messages; a single quiet knock may be polite, a rapid sequence may demand attention, and repeated strong knocks may indicate insistence.

In technical contexts, knocking has specialized meanings. Engine knocking, or detonation, refers to premature burning of fuel in an internal combustion engine, producing a pinging sound that can damage cylinders. In music and performance, knocking can be used as a percussion technique or stylistic effect. The term also appears in phrases such as knock on wood and knock-knock jokes, the latter involving a caller and the classic Who's there? exchange.

Etymology and usage: The verb derives from Old English cnocian; cognates appear in other Germanic languages. The related noun knock is attested in Middle English. Idioms include knock on wood, knock-knock jokes, and knock-out in sports.