When a key is pressed, it sends its associated hammer into motion, and the padded hammer hits a string. If the string is long and thick, the pitch is low; the key is on the left end of the piano. If the string is thin and short, the pitch is high; the key is on the right end of the piano. After striking the string, the hammer rebounds and returns to its original position. The piano is deemed both a percussion instrument because of hammers and a stringed instrument because of strings. Eighty-eight keys.