How do pianos make sound?

Each key on a piano operates a little felt-covered hammer inside the piano, and each hammer is lined up with one, two, or three strings. Each string has been stretched, or “tuned,” to vibrate back and forth at just the right speed to make the sound of a musical note. When someone presses a key, the hammer strikes the string or strings, and the strings vibrate, making a musical tone. The vibrating strings make the sides of the piano vibrate, or “resonate,” at that same frequency of vibration, which makes the sound louder.