After kids have explored all the elements of sinking and floating, then issue a challenge: Engineer a Boat that Floats. In class, we offer a “ship building factory.”
At home with preschoolers, you might offer just a few materials and maybe even a sample to replicate. I might even give them a base that you know will float (like a plastic cup or bowl) and just let them decorate it.
With older kids, you can challenge them to search the house for ideas, and do all the engineering and testing to find working solutions. Some possible materials: some things to help it float – corks, plastic lids, plastic containers, pool noodle chunks or other foam; structural materials like popsicle sticks, straws, aluminum foil, clay, etc. You can’t use water-based glues or tape that gets unsticky in water (scotch tape and masking tape), so you’ll need fasteners like rubber bands, twist ties, string, metal paper fasteners, etc. Here’s pictures of some “boats” in progress.
Testing your boat
While building, it’s helpful to have a small tub of water nearby so you can go through the engineering process: build something, test it, tweak it, test it again and again till you have the best design.
After that, you could test it in the bathtub, or in a kiddie pool, or you could get really adventurous and take it out on a lake or river, where you can set it at the edge of the water, and watch it sail. A few essential tips if you’re taking it out in the wild. Let your child know it advance that there’s always a risk the boat will get wrecked and they should be emotionally prepared for that. Tie a long string to it so it can’t escape and you can reel it back! Have a long stick that you can poke it with if it gets stuck. And be responsible – don’t leave your boat behind – that’s littering and sets a bad example for your child… so, if it’s stuck, it’s up to you to figure out how to get it back.