What Causes Density in Particular Examples?
As a group, discuss each of the following objects/substances in terms of what contributes to their density: 1) a piece of copper; 2) a piece of bread; 3) steam in the air. The sheet, Group Discussion of the Causes of Density is provided in case you want students to draw and think along with the class. For instance, for the copper, because you have a pure, solid metal sample, such as is describe by the first two causes, the mass of the atoms and the structure of the bonds account for the density of the object. But the bread and the steam in the air provide examples of mixed densities, and therefore you must consider Cause #3. Discuss how scientists might picture the various objects inside. Invite the students to contribute to the drawings and to discuss and critique them. Going through the sample substances one at a time, ask students which causes they think contribute to the density of each object. For each substance, ask: • Do you think the first cause, the mass of the atoms, explains
