# Density Cube

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This lab activity allows students to demonstrate their knowledge of density by creating a cardboard cube of a known density. Each lab group has a different density cube to create, thus forcing each group to think for themselves.

Most students struggled with trying to figure out how big the cube should be. Many of them chose the maximum mass (500 grams) and then calculated the volume, which turns out to be enormous, depending on the density. Instead, the most successful groups chose a mass (say, 50 grams) and then calculated the size of cube they'd need to build to hold that mass. This does result in them packing the cube entirely full of bb's, which, if they didn't measure very well, becomes a challenge for them.

I made two example cubes (0.6 g/cm3 and 2.4 g/cm3) to show the students examples. They are typically surprised to see that the 2.4 g/cm3 is the smaller of the two cubes. Most often this is because the students don't really understand the concept of density, especially as it relates to volume. Most students can grasp that two cubes of equal size with different masses have different densities. But to judge the density when there are different volumes is quite a different mental challenge. I made the 2.4 g/cm3 cube by create a 1cm x 1cm x 1cm cube and then filling it with copper bb's.

For the lab, I put out scissors, cardboard, tape, and copper bb's. You can choose just about any item to fill the cubes with, as long as the filler has a density greater than the largest density that any particular group has. Certainly this could easily be done with lead (~11 g/cm3), copper (~9 g/cm3), zinc (~7 g/cm3), etc. I would not suggest aluminum (~2.7 g/cm3), since its density is much lower than the above metals. You want a density of the filler material that is significantly larger than your maximum assigned density so that the students have a chance to underfill their container to obtain a density lower than the original density of the metal.

I checked in each group's results by measuring the LxWxH and the mass, then calculating the density. If they were not within 0.1 g/cm3, I typically had them go back and redo or recalculate.
Total Pages
3 pages
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Teaching Duration
30 minutes
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