Remember, a dead fish can float downstream, but it takes a live one to swim upstream.
W.C. Fields
Why do some things float and some things sink?
The simplest answer is density. Things that are more dense than water will sink and things that are less dense will float.
It’s phenomenal! Aspartame found in diet soda is less dense than sugar found in regular soda. The density of diet soda is around 0.97 g/mL and the density of full sugar soda is around 1.02 g/mL. If you have a bucket of water, floating a can of diet soda in the same water that regular soda sinks is a great phenomenon to introduce density.
There isn’t a student alive who doesn’t love the density column experiment. You find 3 or 4 or 5 or 6 liquids of different densities and pour them into a graduated cylinder, one at a time, densest liquid first. If you’re smart, you’ll be sure the liquids have different colors to make the effect more dramatic.
I’ve been successful using these liquids:
- pancake syrup (density = 1.37 g/mL)
- antifreeze (density = 1.11 g/mL)
- salt water (density = 1.03 g/mL, add food coloring for more fun)
- canola oil (density = 0.92 g/mL)
- isopropyl alcohol (density = 0.786 g/mL)
I suppose you could substitute tap water for the salt water, but that’s less fun. The cool thing about this is that the densities of the layers are different enough that they won’t mix. Of course, each layer is a different color which is even cooler.
A more challenging density column includes liquids that will mix next to each other such as isopropyl and water. A little food dye in one or both of the layers will show them mixing at the surface.
I wrote a density workbook for a fifth grade class including the density column lab and lots of worksheets to practice D=M/V. I think it could be used for older students also.
Of course, in order to measure density, students have to first know how to measure mass and volume. I included a review of mass and volume in the packet, but there are other resources to teach mass and volume that you should check out.
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