paper roll. As we saw, a hollow tube is as strong as a solid and is able to support a lot of weight. As bones grow, calcium and phosphorous are put into the cartilage. They become strong and are able to support and protect our body. Discuss with students ways to keep your bones strong through a healthy diet and exercise.
Elaborate: Set a second book on top of the toilet paper roll. Once again it should easily support the weight. Have students make another prediction about how many books the toilet paper roll will hold before it bends or breaks. Discuss with students why your bones need to be strong.
Evaluate: In science notebooks have students write at one good paragraph about ways to keep their bones strong.