Today we learned about water tension and cohesion… words they might actually remember!  LOL!  Because people—when water molecules are about to break apart from their friends, THINGS GET TENSE!  We also showed lots of other “co” words that meant “together” like “community”, “company” and “co-habitation”.

We started with Dixie cups of water that we brought to nearly overflowing by adding a penny at a time.  Seeing the water bulge out of the cup—above the ledge with nothing holding it—was really cool!

Then they tried this with pipettes dropping water onto a penny.  We saw that two sides of a penny produced different results and we brainstormed about why that might be the case.  One of our students also noted that they had a penny with a different back design and it changed their results as well.  Some of you now have pipettes at home and they might try it on other coins (or just show you on a penny at home).

To further explore the cohesion (or “stickiness factor”) we used a ruler printed on a paper under a plastic sheet to see how far we could stretch a blotch of water.  Some of the students could drag it 14cm before it broke… at least we’re pretty sure it hadn’t broken yet!

Last but not least, we tested the cohesion when the line of water had to bend – which was interesting.

STEM: Water Tension & Cohesion