## Thursday, January 20, 2011

### Measurement Unit: Episodes 5, 6 (Density!)

Following the introduction to volume formulas, my kiddies spent a day or so doing various conversions in class. The wildest is when they found out that it would take 200,000 liter-bottles of water to fill up our classroom! (And that 1 cubic meter = 1,000 liters = 1,000,000 cubic centimeters!! They were amazed by how huge that number sounded, even though they were absolutely convinced that 100 x 100 x 100 = 1 million little cubes inside the "huge" cubic meter.)

After that, I did with my kids today my second favorite lesson out of the entire measurement unit -- density lab! It's actually a two-labs-rolled-into-one sort of thing. I had to set up 6 lab stations. At 3 of the stations, there are irregular containers (two spray bottles of different sizes, and one curvy baby bottle) whose volumes need to be measured using transfer-of-water idea. (I provide them with some extra empty beakers and some bottles of water.) At 3 other stations, there are triple-beam balances, beakers, water, and some object (rock or cube) whose density needs to be measured. They had to practice using the various instruments to gather the mass, volume (either using rulers or displacement method) and to predict which objects would float/sink in water, and then to test their predictions. (They were so excited when their cube floated! It's pretty funny.)

The lesson was kind of hairy to set up (since it had involved borrowing a lot of stuff from the Math & Science Center, and digging up my old supplies of irregular containers and objects), but super fun and easy to run! The labs pretty much ran themselves. I just had to go around and make sure kids were cleaning up after themselves in between rotations and were resetting their scales. In the end, we talked about why metal ships float and why the Titanic sunk. (I had to ask, "Do you guys know about the Titanic??" You know, these kids are babies!! One of them told me that Leonardo DiCaprio is old.) And we talked about whether the object's density would change if we tagged on more cubes. (I had made the cubes out of lego-like manipulatives.) My kids were so smart! Some of them realized that g/cm^3 isn't going to change even if you add more cm^3. I also talked them through what happens if you double the volume of a cube -- what would happen to its mass? (After that, the kids were convinced that the overall density, or ratio of mass and volume, would still remain the same. --You like how I threw in a little math word there?) :)

Anyway, it was really fun! :) I am sad that we're nearing the end of our unit. We only have one more measurement lesson left for the honors kids (regular kids are just a couple of days behind) -- net weight and density of liquids! I'll be sad when it ends, but I am already thinking ahead about shooting Pringles cannons for the next unit on triangles and trigonometry.

(Sadly, I can't seem to eat all of the Pringles fast enough. I'll have to email my kids this weekend and ask them to eat some Pringles over the weekend and to donate some cans, so that we can have spare cannons in case one blows up during class!)