Science Storytime: Surface Tension

Surface tension with Lego blocksFor our Science Storytime about surface tension I couldn’t figure out a good book to use for the subject, so we just skipped the reading section. We talked a little bit about surface tension, trying to tie it back to what we’d talked about when we discussed why bubbles are always round.  The science explanation was kept very short. I thought that this was one of those times where my very young audience was probably better served using this activity as a “what happens” experience rather than a “why is it happening” experience. Teaching science to young children can often get sidetracked by understanding the why of things, when preschoolers are still building up their understanding of  what is happening and how the world works in general.

For our first demonstration, I put Lego blocks in a tin of water and we looked at them floating around for a few moments. Then I added soap into the middle (thus breaking the surface tension of the water) and the blocks sprang to the edges of the bucket. The picture doesn’t really convey the process very well. I got the idea to use Lego blocks from this website.

Next we did an activity that my own preschooler never gets tired of. I poured milk into Surface tension demonstrationindividual tins for each child. We put drops of food coloring into the milk, then cotton swabs to dab soap onto food coloring. This caused the surface tension to break and the colors to swirl dramatically. The children were particularly taken with this activity and repeated it over and over, in some cases often enough that we needed to replace their milk so they could start over. Because the colors mix together, it also became a bonus lesson on color mixing. I have not tried doing this with liquid watercolors yet, but I need to attempt that, as I find liquid watercolors are so much easier to clean up and don’t stain your fingers.


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