Density, part 2
We once again headed down to the kitchen to work on our investigations with density, using the activities from chapter 7 of Inquiry in Action
After a review of last week's work, the kids broke into 4 groups. Each group had 2 clear cups of room temperature water. They also received a little cold water which was tinted blue, and hot water tinted red. They used eye droppers to put this in the cups of room temperature water, and noted where the colored water tended to float (note: I supplied white cardstock to set under the cups to make it easier to see the colored water). Overall, this is a tough activity for kids -- some of them don't have the coordination to gently squeeze water out of an eyedropper, and it's also hard to see where the colors are tending to float. On the other hand, it's an easy activity to set up, inexpensive, and really does show that cold water sinks and warm water rises. And then kids asked if they could drink the colored water, sigh, since we must have a big fuss about eating or drinking just about anything quasi-consumable in this class.
To finish off that concept, I did the ever-popular jars-of-water demo. I once again used my glass jars from Frontera guacamole mix (at this point I've decided these are one of my favorite science tools -- easy to clean, easy to remove the labels). This time I made the hot water yellow and the cold water blue. Photos are from practice at home. I put the hot water on top of the cold water first, using a playing card to hold the water in the jar (I tried an index card, but when index cards get wet they get sticky -- the playing card had a slicker coating on it). As you can see, the colors stayed separate for a while
while I tipped the cold blue water on top of the yellow. Which, of course, instantly mixed.
From there we progressed to the Diet Coke vs. regular Coke in a tub of water. The Diet Coke floats because it's actually less dense. Which worked just great at home BUT when I got to co-op I asked someone else to fill the tub I was using, a clear plastic file box, and leave it on the counter. What I didn't realize is that she filled it with ice cold water. Which, of course, was more dense. So both Cokes sank. But, hey, we had just done a demo about hot vs. cold water, so hopefully the kids realized why it was sinking. Frankly, they were mostly going on and on and on about wanting to drink the Coke.
Anyway, we forged ahead -- I asked how we could get the cans, particularly the regular Coke, to float. Someone suggested salting the water, which was a great idea. But I had brought bubble wrap, which I stuck around the can. I explained that we had increased the volume of the object without increasing the mass by much, and thereby changed the density -- sort of the same way life jackets worked. Then I pulled out 4 clear plastic shoeboxes, which we filled half way with water, a bunch of plastic toys from home (insects, animals, and cars), along with some corks (I got those from the wine cork recycle bin at Whole Foods), some styrofoam (I couldn't find any packing peanuts at home that wouldn't melt in water, so I cut up a styrofoam box that we were throwing out -- this is extremely messy, by the way), some snack size zipper-style storage bags, tape, and rubber bands, and asked them to make "water wings" for their chosen objects. They had a great time with this.
After we dried up from that, and collected some of the models to save, I brought up the idea that metal usually sinks in water but we have metal boats. Our hands-on activity was using modeling clay to make a boat. This involved handing out waxed paper for a work surface, and plenty of paper towels to blot up the water (when clay is wet it gets nasty to model). Sometimes we just threw out the clay and started with fresh. A couple of the kids were obsessed with needing to use waxed paper as part of their design to help waterproof the hull.
Some students did a great job with this, some couldn't get a floatable boat. I was in the latter category. I told them that there are mathematical equations to help with this, but we didn't delve into them. Mostly I wanted them to get the idea that they could change the volume by shaping, and thereby change the density.
Overall, an incredibly messy lesson, but very satisfying.
I would high recommend the Inquiry in Action curriculum to anyone looking for ideas for a grade school science co-op. For that matter, it would be outstanding to do at home with a single child. Annabeth and I have discussed going through either this or the ACS middle school curriculum this summer here at home. It's great stuff.