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Drops of water on a PENNY experiment

Surface tension give water some amazing properties, use them to see how many drops of water fit on a penny. I was able to get to 25 & 31 drops. How many can you get? If you don’t have a penny any small coin.


1) Wash and rinse a penny in tap water. Dry it completely with a paper towel.
2) Place the penny on a flat surface.
3) Use an eyedropper or pipette to draw water and, carefully, drop individual drops of water onto the flat surface of the penny.
4) Keep track of the water drops as you add them, one at a time, until water runs over the edge of the penny. You’ll probably be surprised by the number of drops you get on there.


Now if you want to trick your friends rub a little dish soap on the surface of the penny. As that penny will only get around 10 drops because soap breaks up surface tension.


The Science Behind this experiment:
There are two properties at work in this experiment: cohesion and surface tension. Cohesion is the attraction of like molecules to one another. In this case, the like molecules are the H20 molecules in the water drops.


Surface tension is a special term we use to describe the cohesion between water molecules.


Water’s cohesion and surface tension are special because of hydrogen bonds. Hydrogen bonds are formed by the hydrogen atoms of one molecule being attracted to the oxygen atoms of another molecule.


The cohesion and surface tension of water becomes apparent when the drops of water you add to the penny reach the penny’s edge.


Once the water has reached the edge, you begin to see a bubble or dome of water forming on top of the penny. The bubble shape is a result of the water molecules clinging to one another in an optimal shape (just like the bonds on the surface of a blown bubble).


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