Can You Feel The Tension?
We'll try and regularly update this section to bring you experiments and tests that you can do at home.
Experiment 1 - Surface Tension
A great way to learn about basic water physics. Things you’ll need to have:
Jugs of water
Some cups or bowls
Pepper
Soap
Dry paper clips (wet ones won’t work)
Background:
Pond skaters seem to walk on water, their feet cause the water to bend when they run about but how do they do that?
The experiment:
Make sure your hands are clean, then fill the bowl or cup slowly up with water. Then, carefully put a paperclip on the water surface, it should stay on the surface! Then, you can touch the surface with some soap and watch the paper clip drop through the water.
(If you're having trouble, try bending the centre of the paperclip so that you can hold it without your finger touching the water.)
What you learn: Soap breaks surface tension. The paperclip, like the pond skater, doesn’t float on water; it stays on the skin of water. Soap breaks that skin and in fact, makes the water wetter. One of the reasons we use soap is to make water more wet so we can wash our hands better.
Strong water movements also break the surface, so those pond creatures can only walk on still calm ponds or in the sheltered pools of rivers and streams.
Hands on science:
Here is a good experiment for kids to try on their own.
Fill a cup or bowl with water, then sprinkle some black pepper on the surface, it should float. Then touch the surface with soap and it should disperse or sink.
Why? It’s because as the surface tension breaks, a hole forms where the soap touches the water and the hole spreads to the edges of cup or bowl.
Further work:
Where else have you seen water with a skin on it?
(Think about a glass being really full the brim, it looks curved then. Or beads of water on a waxy plant or plastic surface.)
Image: Kotz
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