Surface Tension of Water

This very cool science experiment can be done very easily with things found around the house.

You Will Need:

• A small clear glass bowl (I used a small pyrex bowl here) 
• A bottle of dish detergent (I used Dawn) 
• Water (cold works best, as hot water has a lower surface tension to begin with)
• Pepper
• A tooth pick

Method:

1.     Fill the bowl about half way with cold water.

2.     Sprinkle pepper gently all over the top of the water. It should cover most of the surface, but if you see more and more flecks sinking to the bottom, stop. Most should float.

3.     Dip the tip of the tooth pick into the dish detergent.

4.     Touch the dish detergent covered end of the toothpick to the surface of the water.

What is happening:

Water molecules reach out in all directions - up, down, diagonally, and sideways.  On the surface of the water, the molecules there have no other water molecules above them to reach up to, so they reach out sideways more than the ones below them. This creates the surface tension of the water, where the connections between the molecules are thicker, like a blanket. When you sprinkle the pepper on the water, the flakes are light enough that the water's surface tension can support them. (This is also how a water strider stays on top of a river or pond). The dish detergent however, lowers the surface tension of the water by creating it's own surface tension when it comes into contact with the water. Now, lighter things that used to rest on top of the water, like the pepper, will either be pushed aside, or will begin to drop down through the water. Heavier things that will also initially remain on the surface of the water, like a small paper clip, or a sewing needle, will just drop through with the lower surface tension of the detergent.

I hope you've enjoyed this experiment! Please visit my website: www.booksofafeather.weebly.com to learn more about Heather, and check out her cool children's books!