You will need: 


  • Milk
  • Bowl or plate
  • Food coloring
  • Soap
  • Toothpick


1.  Pour some milk into the bowl, just enough to cover the bottom.

2. Place 1 drop of each color of food coloring around the edge of the milk.

3. Dip your toothpick into the soap.

4. Touch the soap covered toothpick into the drops of food coloring and observe the result!

What's Going On?

This is a pretty simple experiment to perform – but the results are awesome! And the science behind this experiment is actually a bit complex. 

Milk has something called surface tension. Surface tension is a force that holds the drops of milk together. 

(Have you ever noticed that you can actually fill a glass of water slightly above the rim of the glass and the water doesn’t spill? That’s because of surface tension.) 

In this experiment, the soap reduces the surface tension at the exact point where you touched the milk with your soapy toothpick. That reduction in surface tension causes the surrounding milk, which has a higher surface tension to pull away from the soap. And when this milk pulls away it drags the food coloring with it – creating the dramatic movement of food coloring you observed. 

The fact that the soap reduced the surface tension is important. Soap reduces the surface tension of the milk because it is good at dissolving fats. And that is why we use it to clean our greasy dishes! 

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