Spiced Up

Here's a way to create a visual reminder of what soap does to water's surface tension.

Fill a shallow pan with water. 

Sprinkle the water's surface with a variety of herbs and spices (don't use anything with salt).

Cut a piece of paper to fit in the pan.  Lay the paper on the water's surface.

Pick up the paper and lay flat to dry.

Now, sprinkle the water's surface with herbs and spices once again.

Cut another piece of paper to fit in the pan.  Before you lay the paper on the water, add a squirt of dish detergent to the water. 

Lay the paper on the water.  Pick it up and lay flat to dry.

What differences do you notice between the two trials?  Why did the soap cause such a difference?

The soap reduces water's surface tension.  The herbs and spices, which are normally held on top of the water by the surface tension, now fall into the water.  As a result, the paper, which only touches the surface of the water, doesn't collect very much.