This is the British Museum in London. Many buildings are made of stone. Stone is cut from rock. Rock is a _____ material.

You know that some materials are hard and others are soft. Some break easily but others do not. Some materials are weak and some are strong. Wool is soft, but if you pull it, it is quite strong. A glass vase is solid. It is hard to the touch. But it can break easily - it is weak if it is dropped.