Today we are going to do a simple project making fireworks in a jar. This is cool and quite fun to watch, and a simple lesson in liquid density.
- Glass Jar or Glass (make sure it is clear)
- Small Dish
- Cooking Oil
- Food Dye (3 or 4 colors)
- Fill the glass jar with water, but leave some room at the top.
- Take your little dish and cover the bottom with cooking oil. Add 3-5 drops of food coloring, keeping the drops separate. Take your toothpick and dab the drops of food coloring to break them up into smaller bits.
- Slowly pour the mixture of oil and food coloring into the jar of water and watch the fireworks.
What Is Happening:
We are using two types of liquids, water and oil, which, as the saying goes, don’t mix. You can watch this video that will explain this better than I can. The food coloring is water based, which is why it doesn’t mix with the oil, so it drops down to the bottom of the oil. When we added the oil and coloring to the water jar, the food coloring drops down to the water, which it can mix with, so it dissolves into a pretty stream of color. Why does the water stay below the oil? Density! The molecules that make up oil are much larger than the molecules that make up water. This makes the water more dense, because there are many more molecules.
Experiment On Your Own:
What can we do differently in this project and what do you think will happen? Think of materials, what if we used different types of cooking oil, does the density change, and how will that change the results? What if we filled the jar with a different clear liquid like vinegar or alcohol, would that change how the food dye interacts? It would certainly smell bad. What if we flipped this, put the oil with the food coloring in the bottom of the jar and poured water on top, what do you think would happen?
Here is the video I made for Instagram showing the experiment: