Tie-dye Milk and Surface Tension

 - by KitchenPantryScientist

This is one of my kids’ favorite science experiments of all time and could not be easier to do.

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Food coloring isn’t just for frosting any more!  You will be amazed as you watch the forces of surface tension at work in this “brilliant” experiment.

All you’ll need is a small, shallow dish or plate, milk (2% or whole milk work best, but skim milk works too,) dishwashing liquid, Q-tips and food coloring.

I would recommend putting down newspaper and wearing an old shirt, since food coloring stains. You can make a lab coat from an old button-down shirt, by writing your name on the pocket with permanent marker.

First, add enough milk to cover the bottom of the dish.   In a separate small container, mix together about a half cup of water with a squirt of dish-soap (a teaspoon or so.)  Put several drops of different colored  food coloring into the milk (maybe two drops of each color.)

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Dip a Q-tip into the dish-soap mixture and then touch the Q-tip to the milk.  You don’t need to stir!  The detergent will break the surface tension of the milk and the food coloring will swirl around in interesting patterns, as if by magic.

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Play with it!  You can keep re-wetting your Q-tip with soapy water and touching it to the milk.  If you want to, compare how the experiment works with skim milk versus whole milk.  Sixth-graders will love it as much as two-year olds!

Now,  draw a picture in your science notebook of how the milk looked before and after you touched it with the Q-tip!  Take a picture of it and tape it your notebook!  Describe what happened with words or pictures.

What Happened?  Imagine that surface of liquids is a stretched elastic skin, like the surface of a balloon full of air. The scientific name for the way the “skin” of a liquid holds together is surface tension.  When the skin of the liquid is broken, whatever is underneath will be able to escape, like the air rushing out of a balloon.

In this experiment, the surface of milk is like the elastic skin and dish detergent is what breaks the “skin” of the milk, sort of like a pin popping a balloon.  Food coloring and more milk then escape from underneath the milk’s surface, swirling to the top.

Click here to watch my video on how to make tie-dye milk.

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