February 2016:

Here’s the challenge: Fill a glass with water as full as you can without it spilling over. How many paperclips do you think you can add before the water spills over the rim of the glass?

Materials:

- Box of paper clips or a lot of pennies
- Drinking glass
- Dishwashing soap

You will find that you can add a whole lot of paperclips before the water overflows. Challenge your parent, sibling or friend to the same experiment but for theirs add a drop of dishwashing soap (but don’t let them see you) before they start adding the paperclips. They will find that they are not able to add nearly as many paperclips as you were.

What’s happening?

Water is one of the most polar liquids that we know of. What does that mean and why is that important? Water has a positive end and a negative end, not unlike a magnet. What happens when you put a bunch of magnets together? They all stick together. Water is like that – it’s like the water molecules are holding hands and the water molecules at the surface aren’t letting go of their partners and keeping them from falling over the edge. This is called cohesion. By adding the drop of soap to the water, you break some of that cohesion and the water has less surface tension.

References:

http://www.kids-fun-science.com/water-experiments.html

This experiment is related to the June 2006 ChemShorts article of the Bulletin entitled “Pepper Tension”

http://chicagoacs.org/articles/175

To view all past “ChemShorts for Kids”, go to: http://chicagoacs.org/articles.php?article_category=1

Paul Brandt