The students in Ms. Kahn’s class are learning how to analyze substances according to their properties.

“One important property of a substance is its density,” says Ms. Kahn. “Can anyone tell me what density is?”

“Isn’t it sort of like how massive something is?” says Marian. “I mean, that’s not it exactly, but mass is an important factor in density. It’s hard to explain. Density is sort of how tightly mass is packed into something.”

“Yeah,” Jamal adds, “density is how much mass a certain volume of something has. Say you have two things that are the same volume, but one has more mass. Then the one that’s the same size but more massive is more dense.”

“Right,” says Ms. Kahn. “Density is the ratio of mass to volume. We can write it as an equation, like this.” Ms. Kahn writes d = m/v on the board and then says, “Density equals mass divided by volume. Scientists often compare the density of different substances to water. See if you can figure out the density of water for yourselves.”

Marian and Jamal set out to check the density of water, but each interprets Ms. Kahn’s assignment differently.

Finally, Marian calculates the density of water based on her measurements.

10.13 g/10 mL = 1.013 g/mL               17.91 g/17 mL = 1.054 g/mL

Take the average of the two measurements:  (1.013 + 1.054) ÷ 2 = 1.034.

So, the density of water is about 1.034 g/mL

Which student do you think got the most accurate answer, Marian or Jamal? 

What are some possible reasons for the difference in their answers?

Discussion Question:

How would you have interpreted the purpose of this assignment? How does it relate to the purpose of school?