Here's a chance for you to be a scientist and see something really cool. Make sure you ask an adult before you get started.

Materials

• Whole Milk
• Small dish with a flat bottom (we use a Petri dish in the Lab, but you can use a small pie plate)
• Ruler
• Food coloring (4 different colors)
• Wooden toothpicks
• Liquid detergent
• Optional: Skim milk, buttermilk, cream, half & half, water, oil, pepper, plastic toothpicks, hand soap

Procedure

1. Fill the dish about 1/4 inch high with whole milk.
2. Let the milk sit for a moment until there is no movement.
3. Place one drop of each of the four food colorings in the milk in four different
   locations. WARNING: Food coloring can stain clothing and hands.
4. Here is a diagram to follow:
   
   
   
5. Put liquid detergent on the tip of your toothpick.
6. Touch the toothpick to the milk at the center of the dish and hold the toothpick just off the bottom of the dish.
7. What happens? Make some observations.

Extension

Write a hypothesis about why the colors started moving. Was it the fat or proteins in the milk? Was it the detergent? After you make a prediction, test it out by changing one variable in your procedure at a time. For example, if you think that the experiment works due to the interaction between soap and fat, repeat the experiment once using no soap on the toothpick. Then repeat the experiment a third time, but substitute whole milk with skim milk. Be sure to clean your dish well between experiments.

Here are some suggestions:

• Substitute whole milk with skim milk, buttermilk, cream, half and half, water, or oil
• Substitute a wooden toothpick with a plastic toothpick
• Substitute the liquid detergent with hand soap or don't use soap at all
• Substitute food coloring with pepper

The Science Behind the Effect

Whole milk is a mixture of water, fats, proteins, vitamins, minerals, and lactose. Since milk is made up of mostly water, it shares some of the same properties as water such as surface tension.

If you have ever tried to fill up a cup really high with water, you have seen surface tension at work. A dome of water forms above the rim of the cup. This is because water molecules stick together really well due to an attraction called van der Waals forces.

When you put the toothpick with the detergent into the milk, you break the milk's surface tension, as seen when the colors were pushed away from the center. The detergent then starts mixing with the fat in the milk and breaking it down into smaller pieces.

The movement of the colors shows us that the soap is swirling through the solution distributing the small bits of fat. Because the skim milk does not have fat, the soap is not slowed down and the colors swirl more quickly.

If your data proves our theory wrong or if you have another explanation, please email us your ideas.