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Welcome to Monday! OUR FIRST DAY OF SCIENCE WEEK!! Woo hoo!!! I'm excited, I hope you're excited!!!
All our experiments today involve surface tension. Surface tension can be defined as: '... a phenomenon in which the surface of a liquid, where the liquid is in contact with a gas, acts as a thin elastic sheet. This term is typically used only when the liquid surface is in contact with gas (such as the air).' Reference: https://www.thoughtco.com/surface-tension-definition-and-experiments-2699204 Sounds complicated but essentially the surface tension is where a liquid, eg water, is in contact with the surrounding air, usually on top of a cup, glass or container.
Today I'll be presenting a few experiments to "see" and use the surface tension of both milk and water in different ways. These are simple experiments to try at home with relatively little mess, and using items found in most houses.
If you try out an experiment, don't forget to take a photo and upload it to your Science Week Activity Log in your Google Classroom!
Equipment needed for various surface tension experiments today:
shallow dish/deep sided plate/s
milk
food dye
dishwashing liquid
cotton buds or toothpicks
shallow rectangular dish
tap water
cardboard (cereal or biscuit box works fine!)
scissors
bowl
needle
toilet paper squares
Experiment 1: Marbled milk
What happens when you add drops of food colouring to a plate of milk? Now what happens if you use a cotton bud or toothpick, dipped in dishwashing detergent, and touch the droplets of food dye? We make marbled milk! The detergent does the hard work but the food dye lets us easily see how the dishwashing detergent (or surfactant), reduces the surface tension of the milk as it dissolves the fats and oils in the milk. This causes the surface tension of the milk to weaken so the food colouring can quickly spread out.
Experiment 2: Zooming cardboard boat
Can you make a cardboard boat speed across the surface of the water without pushing it? Yes, you can! If you know how to use the surface tension of the water. Place your cardboard cut out of a simple boat shape on the water, touch the back end with a cotton bud/toothpick dipped in dishwashing detergent, and watch your boat zoom across the surface of the water!
As the detergent quickly reduces the surface tension of the water by breaking down and dissolving the unseen oils in the water, the boat will be moved rapidly away from the spot where the detergent made contact with the water, thereby appearing to zoom across the surface!
Experiment 3. Floating a needle on water?
Do you think it is possible to float a needle on water? It most certainly is! Ordinarily, as a needle is made from steel, it should sink as steel is denser than water. However, it is possible to use the surface tension of the water, and lots and lots of patience, to float a needle on the surface of a bowl of water... Check out my video then have a go yourself!
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