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Supplies:
Dish
Food coloring (water based)
Whole milk
Dish soap
Q-tip or cotton swab
Directions:
Pour milk into the dish so that it covers the surface of the dish.
Add drops of food coloring to the milk. You can do this in a pattern or even draw a picture but try to use at least two different colors.
Dip the Q-tip or cotton swab into the dish soap so that you cover one end.
Dip the soap covered end of the Q-tip into the milk and food coloring and watch what happens. Try moving the Q-tip around, dipping it in the middle or on the edge of the dish.
Make it an experiment:
Try using different types of milk such as skim, 2% or even a non-dairy alternative or using different types of soap such as laundry or hand soap and watching what happens. YOu can even make a record of the patterns by laying a paper on top of the milk and then picking it up and allowing it to dry.
What’s happening:
With this investigation, we are exploring two things: surface tension and the interaction of soap with fats. Milk is strange because even though it looks like it is only made up of one thing, it's actually a mixture of water, fat and proteins. This means that when we are completing this investigation, we are seeing a few interactions. The first is that soap breaks surface tension. Surface tension means how tightly molecules, or small bits of a liquid, hold to one another at the top or surface of a liquid. Surface tension can almost be thought of as a balloon stretching across the top of a liquid. When you add soap, it gets in the middle of these molecules and pushes them apart. We can see this interaction in the way that the color moves out in a ring from the Q-tip at first. At the same time though, we are also seeing swirly patterns and this is caused by the soap and fat. These swirls happen because the soap is trying to bunch together and form a coating around little bits of the fat--something scientists call forming a micelle. Forming these micelles is actually really important and is a big part of how soap works to clean things. These two things happening together is what causes the milk to make the truly cool tie-dye patterns
If you want to see an explanation of this with some wonderful pictures, try checking out the American Chemical Society here.
The Video:
Click here to watch Hannah from Shoestring Science explain and complete this investigation
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