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Minutes from ME

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I am sure you realize what it is we animals have that gives us shape and keeps our insides from falling out - our SKIN! It isn't just solids like us who have skin; liquids have "skin" too. Liquid skin may not be as STRONG as ours it is much more FLEXIBLE since its shape always matches the container holding it. Imagine if we could change into the shape of a milk jug, a soda can, a cereal bowl,......!

I am most interested in the part of a liquid's skin that is exposed to the air and how that liquid SURFACE acts when we mess around with it. Watching and explaining the reactions fascinates me.

The skin of a liquid is held together by the cohesive force between liquid molecules that is called SURFACE TENSION. Use a magnifying glass to look at the edge of a water surface in a glass container, you will see that surface tension tries to pull the water inward towards itself and away from the glass wall. This is also what is happening when rain forms drops on windows instead of spreading all over the glass.

This discussion being scientific, we can experiment with a chemical that just plays havoc with surface tension - the culprit chemical is SOAP which zaps it just about out of existence!


Here's a movie
Quicktime Movie 2000k

  • You will need: a foil tray containing a thin layer of milk, red food coloring, green food coloring, a small dish of liquid detergent to be our soap and a straw to use as a dropper.
  • Now carefully place a few drops of food coloring widely separated on the milk surface.
  • Do the next step slowly and watchfully so that you do not miss the show. Now let one drop of detergent drop into the milk surface away from the color drops.
  • POW!!! Just sit back and watch as the soap destroys the force holding the color drops apart, colorful beauty results. Keep on watching until the action stops, it takes that single soap drop almost a minute to meander through the milk.

Make your own experiment to demonstrate how soap handles particles on your skin. Find a clean tray (or make one from a sheet of foil), add a layer of water and sprinkle some pepper on the surface. Now repeat the detergent drop and surface dip as we did with the milk. Just see that pepper dust scoot away from the soap on the water surface!

Now scientific children can ponder this. Does soap on a liquid's skin act differently than it does on our own skin? Maybe not, the soap spreads through the water on your skin, surrounds the small (or sometimes large) dirt pieces it finds, and separates them from your skin so that the shower water can flush them away. Just imagine - Bathing As A Scientific Procedure!!!!

SOAP POWER describes another soapy experiment. After trying this one with a boat how about trying some other shapes and actions? I can think of a flower shape that could be sent spinning with just one drop of soap!


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