Water Droplets on a Coin

🎂 4 + years ⏱️ 15 min 📍 Anywhere ⭐ very easy

Imagine you are a tiny water droplet that has just fallen from the sky. Your journey takes you to the surface of a shiny coin. But what happens now? How many of your 'water friends' can fit on the coin before it overflows? And why are you holding on so tightly to your friends? You can find out in this exciting experiment! All you need is a pipette, a coin, and of course, some water. Ready? Let's go!

What you'll need

Various coins
Glass of water
Pipettes

How it works

Prepare a glass of water and pipettes. Find different coins, such as a 20-cent or 50-cent coin. Place the coins on a flat surface so they don't wobble.
Take the pipette and draw some water into it. Now hold the pipette over one of the coins and carefully let the first droplet fall onto the center of the coin. Watch closely what happens! The droplet stays as a small, round 'bubble' on the coin.
Now comes the exciting part: How many droplets can fit on the coin? Add one droplet at a time and count along. You'll see the water droplet getting bigger until it almost spills over the edge of the coin. Be careful and focused – it gets more exciting!
Do you also see how the water hangs almost like a glass dome over the coin without running off immediately? Take some photos if you can, or draw a picture of it. It's amazing how the water can hold this shape before it finally overflows.
Repeat the experiment with different coins. Maybe start with a 10-cent coin and then try a 20-cent coin. What do you notice? Does the larger coin hold more water? Or are you surprised by the results?
Write down your results and compare them. You might even want to draw a table to compare the different coins and the number of droplets.
Water droplets stick together. That's why the water stays on the coin and forms a kind of dome. When the dome gets too big, the droplets can no longer hold on. Then the tension breaks, and the water flows down. Have fun experimenting and discovering!