A bell is a simple sound-making device. The bell is a percussion instrument and an idiophone. Its form is usually a hollow, cup-shaped object, which resonates upon being struck. The striking implement can be a tongue suspended within the bell, known as a clapper, a small, free sphere enclosed within the body of the bell or a separate mallet or hammer. Bells are usually made of cast metal, but small bells can also be made from ceramic or glass. Bells can be of all sizes: from tiny dress accessories to church bells weighing many tons.