Why is the piano considered both a stringed instrument and a percussion instrument?

The piano is classified as both a stringed and a percussion instrument because of its internal mechanical design and how it produces sound.

Under the Hornbostel-Sachs system of classification, the piano is considered a chordophone because it relies on strings stretched between two points to create sound through vibration.1

However, it is also categorized as a percussion instrument because those vibrations are initiated by felt-covered hammers striking the strings. When a player presses a key, it activates a complex action that accelerates a hammer toward the string. This method of sound production—striking rather than plucking or bowing—is the defining characteristic that places the piano within the percussion family.1