Paperclips in a Glass

Materials: Clear Container, water, dropper, lots of paper clips

Fill your cup of water as high as you can without it spilling.
Then use a dropper to add the last few drops, so it’s as full as you can possibly get it. 
Have your child estimate how many paperclips he or she thinks will fit into the glass before the water overflows.
Begin dropping the paperclips in one at a time. Older kids may want to keep track of how many they’ve dropped in as they go along. You could arrange your paperclips in piles of tents to keep track easily.
Keep going until the water finally overflows Question to Spark More Curiosity & Critical Thinking How close were you to your estimate? Why do you think so many paperclips were able to fit in the glass?
Here were some comments I caught Lucy making during the experiment: “Why is it not spilling?”” I think it’s because they’re so tiny.”” Look how much paperclips are in it!”” Why don’t the paperclips float?” ~So much thinking going on!
What’s Going On? Drops of water stick to each other. That’s why the surface of the water bulged and formed a dome when you added the paper clips, which kept the water from spilling out. This is called surface tension. Once too many paperclips were added to the cup, the surface tension was broken, allowing the water to spill over.