Project: Drops on a Penny
Video Tutorial: drops on a penny
Have you ever noticed on a rainy day how water forms droplets on a window? Why does it do that instead of spreading out evenly over the whole surface? It all has to do with something called surface tension. Try this activity to learn more!
1. Using a dropper, carefully begin placing a drop of water in the center of a penny, counting as you go.
2. You will begin seeing a dome shape forming in the puddle of drops.
3. Stop when the puddle spills over the edge of the coin.
Repeat the experiment using different types of liquids such as cooking oil, water with dish detergent added, and liquid sunscreen. Surface tension prevents the water molecules from falling out and spilling. You can keep adding water drops until the surface tension is not strong enough to counter the gravitational pull on the water. The size of the drops will vary with different liquids, so the surface tension of each liquid is different. That means the number of drops you can fit on a coin without spilling is different, too!
Sponsored by National Grid.
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