Piano action

A piano action is the mechanism that transfers a key press to a hammer, launching it toward a string and allowing it to rebound without remaining in contact.

Piano key: A lever that a player depresses to operate one note’s piano action. Its downward motion begins the action’s chain of movements.
Lever: A rigid bar that pivots around a fulcrum to transmit or multiply force. Piano keys and action parts use lever motion to transmit a player’s force.
Grand piano action: A piano action whose hammer assembly moves upward toward strings positioned above it. Its gravity-assisted return and repetition lever distinguish it from upright actions.
Bartolomeo Cristofori: An Italian harpsichord maker credited with inventing the piano around 1700. His early piano used a hammer mechanism capable of responding to touch.
Piano technique: The physical methods pianists use to control sound and movement at the keyboard. Finger and arm movements become sound through the action’s response.
Whippen: A pivoting assembly in a piano action that transmits motion from the key to the jack and related parts. It carries the key’s movement toward the hammer assembly.
Pivot (mechanics): A joint or support around which a component rotates. Pivots let the action’s levers rotate through a key stroke.
Upright piano action: A piano action arranged vertically, with hammers moving toward strings positioned in front of them. Its springs help return the hammer because gravity does not reset it as directly.
Cristofori action: The hammer mechanism used in Bartolomeo Cristofori’s early pianos. Its escapement and controlled hammer return established principles retained in later actions.
Piano dynamics: Variations in a piano’s loudness, produced chiefly by changing hammer speed at impact. The action translates differences in key velocity into differences in hammer velocity.

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