The piano is technically a percussion instrument because sound is created by hammers striking strings.

The piano is classified as a percussion instrument due to its internal mechanism known as the 'action.' When a player presses a key, a complex system of levers throws a felt-covered hammer against high-tension steel strings. This physical impact is the defining characteristic of percussion, distinguishing it from string instruments like the violin, which uses friction from a bow.Bartolomeo Cristofori invented the first piano in Italy around 1700. He called it the 'gravicembalo col piano e forte,' which translates to 'harpsichord with soft and loud.' Unlike the harpsichord, which plucks strings, Cristofori’s design allowed for dynamic range based on how hard the hammers struck the strings. This innovation revolutionized keyboard music by providing expressive control through velocity.In the Hornbostel-Sachs system of musical instrument classification, the piano is categorized as a chordophone. This is because it uses vibrating strings to produce sound. However, in the traditional Western orchestral classification, the method of sound production takes precedence. Since the sound is initiated by a strike, it is grouped with drums, dulcimers, and xylophones.Modern pianos contain over 12,000 individual parts, with the hammers being some of the most critical. These hammers are typically made of high-quality wool felt compressed over a wooden core. The speed and force of the hammer strike determine the volume and timbre of the note. This mechanical reliance on striking is why the piano remains the most complex percussion instrument in the modern orchestra.