Science in Sweatpants: Rainy Day Fireworks

If the rain has messed up your 4th of July fireworks plans or you've got some little ones in your group who are just too young to get in on the firework fun, never fear! You can make your very own fire-less fireworks in your kitchen with science.

For the first demonstration, you'll need:

  • Milk
  • A plate
  • Food coloring
  • Cotton swabs
  • Dish soap

Pour the milk onto the plate, just enough to cover the bottom. Next, gently drop a few drops of food coloring into the milk. Be careful not to mix the food coloring into the milk. 

Dip one end of your cotton swab into the dish soap, then place that end in the center of your milk. 

Instantly, you should see the food coloring swirl outwards. Almost like it's being carried by an invisible current!

To understand this experiment, we need to know some things about milk. All liquids at rest, including our milk, have something called surface tension. The liquid's surface molecules are holding onto each other more tightly than the molecules beneath the surface. Also remember that milk contains water, fats, and proteins.

Soap molecules have two sides, a hydrophilic side, and a hydrophobic side. The hydrophobic side is attracted to fats, oils, dirt, etc. The hydrophilic side is attracted to water molecules. 

When washing our hands with soap, one side of the soap molecule attaches to the dirt and oil and the other side of the soap molecule attaches to the water molecules and carries all that gunk away. 

When we place our soapy cotton swab in the milk, two things happen. Soap breaks the surface tension of the milk and the hydrophobic side of the soap molecules instantly attaches to the fats in the milk, spreading outward. This process happens without the food coloring but since we added those food coloring droplets, we get to see the colorful swirls. 

For the next demonstration, you'll need:

  • A glass of water, ⅔ full
  • Cooking oil
  • An extra glass
  • Food coloring
  • A fork

First, fill your extra glass with a few tablespoons of cooking oil. Add a few drops of food coloring. Notice the food coloring doesn't mix with the oil. That's because the food coloring is mostly water and oil and water don't mix. 

Use your fork to break up the food coloring drops into smaller pieces. 

Next, add the oil/food coloring to the water. Because oil is less dense than water it'll float to the top but the food coloring droplets will sink down towards the water in the glass. After a few minutes, the food droplets will dissolve into the water, making our own little firework show in a glass.

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