Piano is a stringed keyboard instrument. The strings of the piano are struck by wooden hammers that are coated with soft materials. It is played using a keyboard, which is a row of keys/ levers that is supposed to be pressed down or stroked with the fingers and thumbs of both hands to cause the hammers to strike the strings. It was invented by Bartolomeo Cristofori around the year 1700 in Italy. It usually has a protective case made of wood, surrounding the soundboard and metal strings, which are strung under great tension on a heavy metal frame. Playing one or more keys on the piano's keyboard causes a wooden or plastic hammer to strike the strings. The hammer rebounds from the strings thereby letting the strings to continue to vibrate at their resonant frequency.