Editing Tie Dye Milk (section)

== Why This Works ==

''Surface Tension'' is the attraction between atoms and molecules at the surface of a liquid. The surface tension of a liquid can be affected by what is dissolved in it, as well as by what is added to it. Whole milk has some fat in it, as well as protein and sugar. The protein and sugar increase the surface tension of the milk, but the fat in the milk increases the surface tension the most. This is why it can be hard to rinse out all the milk from a container or wipe it all up if it is spilled; the fat is really good at clinging together, and so it will resist being rinsed away or wiped off. Soap, however, is a ''Surfactant'', meaning that it is good at reducing the surface tension of a liquid. This is because soap will bond with the particles in the milk and pull them apart, weakening the surface tension and making it easier to clean.

The food dye, when first dropped into the milk, doesn't move much because the milk has high surface tension. It can't disperse through the milk because the fat molecules are holding it in place, so we just see the dots where it was dropped. When the soap is put in the milk, however, the food dye starts moving! This happens because of the soap breaking the fat and pulling it apart, which causes the rest of the liquid to move and pulls the food dye along as well!