Density Curriculum

Section 3—Lesson 10: How Does Mixed Density Contribute to Overall Density?

Understanding Goals

Subject Matter

• A third cause of differences in density is mixed density.
• There are different ways that density can be mixed, for instance, when gas molecules are spread out with other molecules in between; when something is hollow inside or has "air pockets," and so is a combination of air and the material around the outside.
• Mixed density is usually thought of at the macro-level, for instance, as two or more substances or materials (such as water and carbon dioxide in the case of carbonated beverages).
• There are some instances of mixed density at the micro-level, such as certain plastics (polymers) that have a molecular structure that allows gases to fit in between the molecules.

Causality

• Density has multiple contributing causes. Not every cause is involved in every situation where density is in play.
• You can't compare objects by using just one of the causes alone. It will leave out other important relationships that could contribute to the resulting density. You also can't assume that every cause contributes significantly to differences in density in every situation.