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The detergent lowers the surface tension of the water so it is not strong enough to stay in a dome and it will run off the five cent coin



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The detergent lowers the surface tension of the water so it is not strong enough to stay in a dome and it will run off the five cent coin.
Get the students to repeat this with another liquid: milk/lemonade/oil/orange juice and come back and combine the results.
Questions to ask them:

  • What is surface tension?

  • Do you think that the surface tensions of the liquids are the same?

  • Why do you think a bug can stay on top of the water?

  • Why can the five cent coin hold more drops of some liquids than of others?

  • How does surface tension and density differ?

  • Were your predictions correct? If not why do you think it was different?

  • Can you think any ways you have experienced surface tension?

2. Magic Milk

Give each student a Petri dish with milk in it. Put drops of red, yellow and blue food colouring in the milk to make a triangle. Ask the students to predict what will happen when detergent is added to the middle of the Petri dish.
Get them to put 4-5 drops of detergent into the middle and record what they see. They can draw a picture in their notebooks or on the worksheet.

Ask them what they think is happening.






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