Super Cool Surface Tension

winter
Creative Commons License photo credit: shioshvili

Did you know that water is sticky?  It may not look sticky, but water molecules love to stick together.  Water molecules pull and tug on each other from all directions.

Look at a glass of water. A special stretchy “skin” forms at the top of a glass of water because the molecules are pulling from the sides and from below, but not from the top.  This “skin” is known as surface tension.  Surface tension allows the water level to get higher than the walls of the glass without spilling!  Let’s put this to the test.

Materials:
Drinking glass
50-100 pennies
Paper towels

Procedure:
1. Fill a glass to the top with tap water.
2. Set your glass on a paper towel.
3. Carefully add pennies one at a time.  Be sure to keep count. 
4. Observe the water at the top of the cup.  Eventually it will begin to bulge out.
5. Add pennies until the water begins to drip over the edge of the glass.  How many pennies were you able to get into the cup?
6. Now, remove all of the pennies and get a new cup of tap water.  This time add several squirts of dishwashing liquid to the cup and try the activity again.
7. Were you able to add more pennies or did it hold less?  What do you think is happening?  Research and find out!

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