A bell is a resonant metal object in the form of a cup hung from its closed end (the head), which rings when struck with a "clapper" near its rim. It is used ritually to give audible time signals and as a warning device. Modern bells are cast in bell metal (bronze with a high tin content, used because of its sonority) to carefully computed designs so that the correct mix of fundamentals and overtones is produced when the bell is rung.