 My name is Joyce and I'm a Yale 2020 intern at the San Francisco Public Library. Today I will teach you how to create an amazing explosion of colors using milk. Once we've witnessed the school display of colors zooming across the surface of the milk, I will go over the signs behind the school trick. But first, let's go over the materials we will need for this experiment. We will need some whole milk, some food coloring, a cotton swab, dish soap or detergent, and a shallow dish tray or a pan. Now we can start. First we will thin layer of milk that is just enough to cover the bottom of your dish. You might have to wait for it to settle in. Then choose the colors you want to use in your art and squeeze a couple drops of food coloring on top of the milk. Now get a cotton swab and place a drop of dish soap on it. Then place that same end in the middle of the milk and watch as the colors explode across the dish. Now this works. Why do you think the colors try to cross the milk like that? Don't worry, I will explain. It contains mostly water, but also includes proteins, minerals, fats and vitamins. Because it is mostly water, it holds one of the same properties as water. The property of water is that it has strong cohesive forces, meaning water molecules are attracted to other water molecules. This is due to its ability to form hydrogen bonds with each other. A hydrogen bond is a weak interaction that forms between a hydrogen which has a partial positive charge and a more electronegative atom like an oxygen. Electronegative means electrically negative. This means that the hydrogen of water has a partial positive charge, so it is attracted to the oxygen in water because of its partial negative charge. These qualities of water result in cohesion, which is a liquid surfaces tendency to resist rupture when placed under tension or stress. Because the molecules of the liquid underneath the surface draw the surface molecules towards the bulk of the liquid. As a result, milk has a high surface tension and is able to support the dye molecules centralized on the surface. However, the surface tension can be broken with a surfactant called soap. A surfactant is a compound that lowers the surface tension between two liquids. Therefore, when a drop of soap is added to the milk, the surface tension is reduced, allowing the particles of the milk and the color molecules to move freely, creating the visual display that we see. In addition, a second cause of interaction is due to fat molecules and soap molecules. So factants have a hydrophilic side, which is water-loving, and a hydrophobic side, which is water-fearing. Soap is used to clean because its hydrophobic side attracts the oil's well-to-hydrophilic side, bonds with water. The water we use to wash the soap away also washes the oils and fats. So when we put the soap in the milk, soap molecules are moving around and bonding with fats, causing particles to move around. During this movement of soap and fat molecules, the food coloring molecules are also being moved around. A lot of us do witness this cool display of colors across the surface of the milk. As the soap becomes mixed in with the milk, the movement slows down and the dye stops moving. And that's all there is to it. Unfortunately, the milk will soon mix in with the soap and you won't be able to see the fireworks anymore. However, you can do this experiment as many times as you want. Just make sure that each time you dispose the milk down the drain and you clean up after yourself. And if you decide to do this experiment right away again, then make sure you wash the dish with warm water so there isn't any lingering soap. Because if there is, it will affect your ability to complete the experiment the next time. Thank you so much for watching and make sure you check out the other STEM challenge yourself videos from SFPL librarians and Yale interns. Bye!