Water drops on a coin
Join me for a fun and simple experiment that shows the amazing properties of water. Using just a coin, a cup of water, and a dropper, we’ll see how many water drops can fit on top of the coin before spilling over. This experiment is a great way to learn about surface tension – a special force that makes water molecules stick together. It’s easy to do, fun to watch, and perfect for anyone curious about how water behaves. Let’s discover the wonders of water together with this straightforward experiment!
Materials:
- A cup of water
- Coins
- Pipette or dropper
What to do?
- Place a coin on the table.
- Start gently dripping water droplets onto it.
- Count the drops.
How does this happen?
Between the water molecules, there are special connections called hydrogen bonds. These bonds are relatively strong compared to bonds between other liquid substances and cause the water molecules to “prefer” to bond with each other rather than with the air. On the surface, the attraction forces between the water molecules create a kind of “skin” that covers the surface, a phenomenon called surface tension of water. This skin is relatively strong and allows the water to form a fairly high dome that even slides a bit from the sides of the coins before the water spills from the coin.
Fun fact:
Soap knows how to weaken the bonds between water molecules and actually break the surface tension, like a pin stuck in a balloon. The “skin” on the surface of the water tears and is pulled to all directions.
What do you think will happen if we try to drip water with a little soap onto a coin? How many drops can we drip onto the coin without them spilling?
Continue to explore: Try performing the experiment with different liquids: milk, salt solution, alcohol, orange juice, oil, syrup, etc. Write down for each liquid how many drops you dripped onto the coin before they spilled. Why do you think there are differences?
We’d love to showcase your creativity!
Share pictures of your experiments with us, and together, we can inspire young scientists everywhere!
