My kindergarten students believe that small objects are always light and big objects are always heavier. How can I address this misconception?
—L., Wyoming

Excellent question! This is a major misconception many adults have about density: the characteristic relationship between the mass and volume of materials.

I think the best way to tackle this is to have a hands-on activity. Buy or make identical-sized blocks, cylinders, or balls of different materials: plastic, wood, soap, iron, aluminum, styrofoam, plasticine, and so on. Although we are saying size, we are actually referring to volume.

Using the same series of materials, make shapes in larger sizes. The more sizes you can get the better.

Have students hold the same-sized cube of iron and aluminum in their hands. They should observe a difference albeit subjective. Use a double-pan balance or make a simple teeter-totter device to compare masses of objects objectively. Have them rank the different blocks from heaviest to lightest.

Can they balance a small, “heavy” object with a few “lighter” objects? At some point, the students should realize that many “light” things (or a single larger “light” item) can have the same weight (mass) as a smaller “heavy” object.

Now blow up a balloon! How does that compare to any of your other materials? It’s bigger, but I bet it’s lighter than almost everything else.

Hopefully this will lead to a better understanding of the density of different materials.

Hope this helps!