For day 15, students completed a density lab and whiteboarded their results (this was done over a double-blocked lab period). For the density lab, students were asked to find the relationship between mass and volume for a set of PVC cylinders and a set of aluminum cylinders (generic density kit). Students then graphed their data, found the lines of best fit and calculated the slopes. During the board meeting, I asked questions like, “if you had the same volume of aluminum and PVC, which would be more massive?” or the converse, “if you had the same mass of aluminum and PVC, which would take up more space?” in addition to the typical “what’s the relationship” type questions. On the whiteboards you can see that I had students draw in the line for water (knowing that 1 mL of water has a mass of 1g). Students then hypothesized from their graphs that the aluminum and PVC pieces would sink if dropped in water. Students tested their hypothesis using the large tub of water I keep on my demo desk while we are going over density. I then had students draw particle models for the PVC and aluminum if they had the same volume of each. Students concluded that the aluminum either had to have bigger particles or more particles than the PVC to account for the different mass to volume ratios. Finally, at the end of the discussion, I gave the mass to volume ratio (slope) the name “density”.