For one of my grad school classes on Tuesday I had to present a science demonstration. After some serious googling, I found this demonstration:
Cat’s Meow Demo:
Overview: Oil causes the food coloring to circulate in the milk, making swirls of color
Equipment: Milk in a glass, Food colors, Oil
How to do the experiment: Put milk in a glass or cut the lid off a carton. 2% or higher fat content works the best.
Place one drop of each color of food coloring in each corner of the carton or near the sides of the glass.
Place a drop of oil in the middle (I put it in the glass on the right). Be careful not to move the glass or to shake the table. After a short time the colors swirl and mix, it looks really cool.
Explanation: This is caused because milk is mostly water and some fat. The oil is only soluble in the fat, not in the water. The oil creates a current which causes the colors to circulate and mix.
Note: The milk must not be disturbed for the experiment to work properly.
This is a way fun demo, for sure. When doing it with kids, you can do it on paper plates. The large surface makes for more space to see the “coolness.” Kids like cool things. But they like things with more coolness, more.