Holly goes to the playground. She climbs up onto the bars. The bars must be strong to hold Holly. The bars are made from _____.

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.