Reflection: Lesson Planning Density Lab (Volume by Formula) - Section 3: Lab (Student Activity)


The first time I taught this activity the density cubes where exposed. Meaning that the identity of each cube could be reasonably approximated by looking at the exterior. For example, instead of the students calculating the density of the brass density cube (as had been planned) the students picked the density cube that had a brass color which obviously had some heft to it and identified it as brass without determining mass and volume to calculate density. The lab was over within a few minutes, none of the groups did any measurements, and the students had identified the density cubes with 90% accuracy using only sight and feel. Needless to say this activity was a failure!

The next year I had learned my lesson and carefully wrapped each density cube in electrical tape. The students couldn't easily identify the cubes and were forced to work the activity as planned. The problem now was that the electrical tape affected each cube's mass, which in turn altered the cube's overall density. When the kids tried to match their calculated densities to known densities many students got the wrong answers, since the chart didn't match up. Another epic fail!

The third year I assigned this lab I had my students subtract the weight of the electrical tape (3.7g) before calculating density of the cubes. This way the densities come close to the published values. I remind my students that there is often a difference between experimental and theoretical values and they may not be able to calculate exactly accurate values for density.

I recommend to my students to first calculate all the densities of the cubes, then use those values to make approximations of which material the cubes are. With these changes the lab is successful and the students gain experience measuring mass and volume to calculate density.

  Why hide the identity of the density cubes
  Lesson Planning: Why hide the identity of the density cubes
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Density Lab (Volume by Formula)

Unit 7: Density and Buoyancy
Lesson 2 of 6

Objective: Students will be able to calculate the density (D=m/V) of multiple cubes with the volume formula (V=lwh).

Big Idea: Learning to calculate density is done best with experience.

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1 teacher likes this lesson
Science, buoyancy, density, displacement
  120 minutes
density lab
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