Fresh Water, Salt Water

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This activity from Travis’s January issue of High Five magazine provided a nice dose of STEM learning, alongside the usual monthly craft. We’ve done a similar experiment before, but liked the set-up for this version!

Fill 2 large clear glasses with 1 and 1/2 cups warm water each.

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Add 1/3 cup salt to one cup, and stir until dissolved.

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The instructions said to tint the other cup blue with food coloring so you can tell them apart. Because the salty cup is cloudy, this step isn’t really necessary, but blue water is cool, so why not!

Now add the same object to each of the two cups, and observe any differences. We tried the magazine’s suggestions of aluminum foil balls, which floated to the top in both versions.

Next we tested plastic dinosaurs. Both sank. Hmm, no difference!

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Finally, when we tried tomato slices, the tomato in the salt water seemed to pop above the surface with more buoyancy.

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But why hadn’t the others been different? We added more salt to the salty cup, liberally pouring in and stirring. After two more tries, we had a crayon that floated!

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The crayon in the opposite cup, down at the bottom, helped illustrate buoyancy best for Travis.

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Overall, he loved the set-up and scientific nature of the project, plus adored pouring the salt. Great for budding scientists.

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