College-Prep Physics: In the past, I never spent much time on this, since students had gone through these terms every year since middle school. I usually asked for definitions of mass and weight just before starting the traditional mass/weight lab, and left it at that.
This year, I asked each group to define mass, weight, and volume on a whiteboard. I collected their ideas:
Then I brought out these 5 objects (that’s a block of wood on the moon, by the way):
And asked them put the objects into groups: which ones had the same mass? the same weight? the same volume?
They made the obvious groupings:
- the wood block, the foam block, and the wood block on moon all had the same volume
- the wood block and the wood block on the moon had the same mass
Lots of good conversation happened between the students. Then, to check their predictions, I brought out the double pan balance and the spring scale. We talked about what each instrument measures and how it works.
Kids were quite surprised when they saw the wood block and the “silver metal” balanced:
There is something visually striking about watching it balance — more memorable than just massing both items on an electronic or triple-beam balance. They were also equally surprised when the foam block and the “black metal” balanced:
I asked students to draw particle diagrams to show what the molecular structure might look like to produce this outcome of different volumes with the same mass. Then we went back and refined our original definitions of mass, weight, and volume.
NGSS Science and Engineering Practice #6: Constructing Explanations