Piano hammers rebound and strike strings multiple times per note

Evidence

In the piano, the strings are struck with a hammer covered with felt. The hammer gets its speed from pressing a key on the keyboard. The hammer hits the strings usually two to three times, depending on the force applied to the key. A similar effect is seen when the membrane of a drum is struck with a stick. This method of excitation is also non-linear, since the movements of the string or the membrane affect the excitation during the second and third hits. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 669