Science Saturday Challenge #9

Surface Tension

Water is an amazing molecule for many, many reasons, one of which is it's incredible surface tension. First read this article: Sticky Water from the Exporatorium to get an idea of why water has such adhesive abilities.

A great book about water, including surface tension, with stunning pictures is A Drop of Water by Walter Wick.

These experiments are easy to do and visually impressive, both of which make for favorite science experiments in our house!

Materials
A small bowl of water
Pepper
Liquid soap (for hands or dishes)

Procedure
Sprinkle pepper onto the surface of the water until it pretty much covers it.

Dip a clean finger into the bowl of water, and Ds#2 and Ds#3 are doing in the picture below.



Now rub your fingertip with a little of the liquid soap and dip it back into the center of the bowl.



Now try the experiment with milk and food coloring for a more dazzling display!





Soap has a polar "head" that attracts the hydrogen bonds of the water, but also has a hydrophobic "tail" that stick up at the water surface. When the water bonds to the soap the tails break up the surface tension. That makes the pepper and the food coloring scatter, and gets dirt off of surfaces!