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Science in Sweatpants: Rainy Day Fireworks
In the latest edition of Science in Sweatpants, meteorologist Chelsea Andrews shows you how to create colorful fireworks without a fire in the kitchen.
Austin, Texas – If the rain has messed up your July 4th fireworks plans, or you have some small children in your group who are just too young to join the fireworks fun, fear not! Science can help you make your own fireworks display without a fire in your kitchen.
For the first demonstration you will need:
- milk
- A plate
- Food coloring
- cotton swab
- Washing-up liquid
Pour the milk on the plate, just enough to cover the bottom. Next, carefully drip 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 detergent and place that end in the middle of your milk.
Immediately you should see the food coloring swirl outward. Almost as if carried by an invisible current!
To understand this experiment we need to know a few things about milk. All liquids at rest, including our milk, have what is known as surface tension. The surface molecules of the liquid stick together more tightly than the molecules below 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 hands with soap, one side of the soap molecule sticks to dirt and oil and the other side of the soap molecule sticks to the water molecules and carries all the dirt away.
When we put 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 immediately binds to the fats in the milk and spreads outwards. This process takes place without the food coloring, but since we’ve added these food coloring droplets, we can see the colorful swirls.
For the next demonstration you will 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. Make sure that the food coloring does not mix with the oil. This is because the food coloring is mostly water, and the oil and water do not mix.
Use your fork to break the drops of food coloring into smaller pieces.
Next, add the oil / food coloring to the water. Since oil is less dense than water, it floats up, but the droplets of food coloring sink towards the water in the glass. After a few minutes, the food droplets dissolve in the water and make our own little fireworks in the glass.
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