High Quality Content by WIKIPEDIA articles! The piano action mechanism, or the key action mechanism, or simply the action of a piano or other musical keyboards, is the mechanical assembly which translates the depression of the keys into rapid motion of a hammer, which creates sound by striking the strings. Action can be referred to a pianos or other musical keyboards, including stage pianos and synthesizer. The key action mechanism determines weighted keys feeling, that is the feeling of the heaviness of the touch of the keys.