Milk Planets

I opened the fridge today and found we had a ton of milk. Now, this is an odd occurrence, but I had an idea on how to make the most of it. We have been collecting bottle lids all summer, planning to use them to make milk planets. It doesn't take much, and it has a little science lesson to go along with it.

You start with a little milk (whole is better than skim - see the science below for why), three or four food colors, several lids, some dish soap and a few cotton swabs.


We had saved enough lids for the kids to get five lids apiece. They poured in a little milk, just enough to cover the bottom of the lid, then added a drop or two of each color they wanted for a planet. Then you dip the cotton swab into the soap and stick it into the milk.

The food coloring will immediately repel away from the dish soap on the cotton swab. If you twist the swab, you can get the colors to twirl around as well.

Try different color combinations and amounts, as you can get some really fun patterns to emerge. Once you have a look you like, take some pictures to print for your kids to cut out and make their own solar system, or place them on a piece of black construction paper to give the appearance of floating in space!




Now here's the science part of it all:

When you first add the food colors, the milk doesn't want to let them in. The soap however, breaks the surface tension of the milk and allows the color to flow freely through it. By turning the cotton swab, or by putting it in at different places, you can control where the colors then go.

Surface tension is what causes milk or water to bead on a smooth surface. If you look at a glass of milk closely, you'll see what looks like a thin skin on the top of the milk. The soap breaks up the fat molecules making up this skin and allows the food coloring which is less dense to disperse throughout. The more fat in the milk, the more action you'll see with the food coloring.