Do you remember our lolly stick races? They are a great way to explore surface tension, but this activity is even easier!
Surface tension activity with toothpicks
- Cocktail sticks or toothpicks
- A Bowl
- Washing up Liquid /Dish soap
- A large bowl
- Fill the bowl with water and let it settle for a few minutes.
- Carefully place the cocktail sticks on the top, if you can, try and get them to form a triangle.
- Add a drop of washing up liquid, and watch what happens.
This activity is a simple demonstration of surface tension. When you have a container full of water, the water molecules below the surface are pulled together equally in all directions, but those on top are pulled together more tightly, as they don’t have water molecules above them, this draws them together to form a kind of ‘skin’ which we call surface tension. When we added washing up liquid we disrupted the arrangement of the water molecules which decreased the surface tension inside the triangle of sticks.
Water molecules move from areas of low surface tension to high surface tension and so the sticks moved.
Don’t worry if that explanation seems like too much for your child. I don’t always explain the full scientific principles to my children, but watching and taking part in activities like these really does encourage children start to question why things happen, and the concepts we introduce will become start to make more sense to them as time goes on.
More surface tension experiments
Try racing lolly sticks across a bath or large container of water.
Raising Lifelong Learners has a great activity for making a paperclip float using surface tension.
If you enjoyed this investigation why not try one of my other easy science experiments!