Although an acoustic piano has strings, it is usually classified as a percussion instrument rather than as a stringed instrument, because the strings are struck rather than plucked (as with a harpsichord or spinet); in the Hornbostel-Sachs system of instrument classification, pianos are considered chordophones.
The black keys are for the "accidental" notes (or "black notes"), which are the sharp and flat notes, which are F#, G#, Bb, C#, and Eb, which are needed to play in all twelve keys. The strings can be sounded when the keys are pressed or struck, and silenced by a damper when the hands are lifted off the keyboard.
These vibrations are transmitted through a bridge to a soundboard that amplifies by more efficiently coupling the acoustic energy to the air.
When the key is released, a damper stops the strings' vibration, ending the sound.
Although the piano is very heavy and thus not portable and is expensive (in comparison with other widely used accompaniment instruments, such as the acoustic guitar), its musical versatility (i.e., its wide pitch range, ability to play chords with up to 10 notes, louder or softer notes and two or more independent musical lines at the same time), the large number of musicians and amateurs trained in playing it and its wide availability in performance venues, schools and rehearsal spaces have made it one of the Western world's most familiar musical instruments.
An acoustic piano usually has a protective wooden case surrounding the soundboard and metal strings, which are strung under great tension on a heavy metal frame.
Pressing one or more keys on the piano's keyboard causes a padded hammer (typically padded with firm felt) to strike the strings.The hammer rebounds from the strings, and the strings continue to vibrate at their resonant frequency.