Wet Money

Water | 10-20 minutes

In this activity, students will explore surface tension by filling up a coin with water! (Crazy right?)

Materials Needed

Per student:

• Penny, nickel, dime and quarter

• 1 cup of water

• 1 dropper or pipette

• 1 printout

Optional:

• Magnifying glass

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Steps:

1. Lay the coins out on a table or other flat surface.

2. Write an estimate on the printout for how many drops of water will fit on the penny.

3. Using the dropper or pipette, put a drop of water on the penny.  

4. Continue adding drops of water, counting how many you can put on top of the penny before the dome of water on the top breaks and the water runs off.

5. Write down how many drops you successfully piled on top of the penny.

6. Do the same thing for the other coins, writing down the results.  As you go, closely watch the way the water piles up on top.  If you have a magnifying glass, you can really get a good look.

7. Compare your results with those of the other students.  Did everyone get the same results?  What could cause variations?

Explanation:

Water is a polar molecule. That means that it has a positive end and a negative end. The negative end of one molecule is attracted to the positive end of another molecule (similar to a magnet). That makes the molecules stick together tightly. The molecules that are sitting on the coin are pulled inward and they stick together so that they form a dome. This is called surface tension. Eventually, though, gravity overcomes this force and the dome breaks, spilling water over the sides of the coin.

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Real World:

The domes that you see on the coins are caused by the surface tension of the water. The dewdrops and raindrops form on plants the same way!  

Some insects can walk on water due to the spring-i-ness of it.

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