Originally posted on March 8, 2010
When beginning a unit or lesson on water, I like to ask my students to give me as many words as they can think of to describe water. I make a list on the board and at the end, add one or my own: sticky. Students look at me like I've lost my mind, but once they start on this experiment, they start to understand my description - the water drops stick to one another. A great introduction to the properties of adhesion, cohesion, and surface tension.
Encourage students to make up their own experiments. For example, which side holds more, heads or tails?
After going through the activity once, you can mess with your students a bit - put a little liquid soap in their water supply, or rub a little soap on the penny. The soap interferes with the surface tension and the pennies can't hold nearly as much water.