Water Surface Tension Experiment for Kids

Water Tension Experiment for Kids

Has your child ever asked how water can take different forms and shapes such as raindrops or puddles? The liquid molecules in water change with outside forces such as gravity. You can observe water tension on coins with this fun water surface tension experiment.

Supplies

• Coins
• Straws
• Water
• Plate
• Food Coloring

Water Tension Experiment

We’re using food coloring with this experiment so kids can see how the molecules in the water move when the surface tension is disrupted. While liquid molecules don’t necessarily move in the same pattern as colored water, it’s a good way to explain how molecules pull together or apart based on outside forces.

1. Mix two bowls of water and food coloring. We used blue and yellow coloring so when mixed during the experiment the water turned green.
2. Dip one end of a straw into the blue-colored water and place your thumb over the other end to trap the water inside. Slowly release your thumb and let the water pool on a coin.

Observe the water as it pools on the coin. The boundary liquid molecules pull towards the edges of the coin while the surface molecules pull towards each other at the center. This makes the water form a bubble-like shape on the coin. When the tension of the water is disrupted it will spill over the edges of the coin.

Experimenting with Liquid Molecules

1. Using a separate straw and the second bowl of colored water add drops to the water on the coin. Where does the new water go? The molecules mix and pull together making the two colors blend into the green.
2. Set up a row of coins and add different colors of water drops to each, forming surface tension. Use a toothpick to pull water from the first coin to the second coin. Can you pull the water all the way to the end of the row of coins without breaking the tension?
3. Add water around a coin on a plate. Next, add a few drops of differently colored water to the coin. Use the toothpick to disrupt the water surface until the tension breaks and the water spills over the edge of the coin. The colors will begin to mix into green showing how the liquid molecules spread once the surface tension is broken.
4. In this last observation, dip the straw into the water and place your thumb over the other end. Lift the straw out of the water and observe the drop of water at the end of the straw. Your thumb is creating suction to hold the water in but the air molecules are also causing the liquid molecules to pull together forming a drop at the end of the straw. Gravity is pulling the drop-down and if you remove your thumb from the straw the tension will break and the water will drop.

More Water Science for Kids

Layering Liquids

Learning about the Water Cycle with Salt

Racing Water Drops