The Rainbow in a Jar
Pour them carefully into a glass, and instead of mixing together, they'll stack in separate layers — heaviest at the bottom, lightest at the top. It looks rather odd at first, but it's just physics doing what physics does.
You know how oil floats on water? That's density at work. Different liquids weigh different amounts, even when you've got the same volume of each. Pour them carefully into a glass, and instead of mixing together, they'll stack in separate layers - heaviest at the bottom, lightest at the top. It looks rather odd at first, but it's just physics doing what physics does.
Turns out - it creates something beautiful.
What You'll Need
- A clear glass or jar
- Honey
- Dish soap
- Water (add a drop of food coloring to make it visible)
- Vegetable oil
- Rubbing alcohol (add a different food color)
- A steady hand and patience
What You'll Do
Here's the secret: liquids have different densities, which means some are heavier than others. The heavier ones sink to the bottom, and the lighter ones float on top.
Pour slowly and carefully (this is key—if you rush, the layers will mix):
- Start with honey at the bottom (it's the densest)
- Gently pour dish soap on top
- Add your colored water
- Slowly add vegetable oil
- Finish with colored rubbing alcohol on top
Pro tip: Pour each liquid over the back of a spoon held just above the previous layer. This helps prevent mixing and keeps your rainbow crisp.
What You'll See
Five distinct layers, stacked like a rainbow. Honey at the bottom (golden), dish soap (usually clear or blue), colored water, oil (clear), and rubbing alcohol (whatever color you chose) on top.
It looks impossible—like the liquids should mix together—but they don't. Each one stays in its own layer because of density.
Why It Works
Think of density as how tightly packed the molecules are. Honey molecules are packed very tightly (dense and heavy), so honey sinks. Rubbing alcohol molecules are loosely packed (less dense and light), so it floats on top. Each liquid finds its place based on how heavy it is.
Try This Next
Once you've got your rainbow jar:
- Drop in small objects (a grape, a piece of plastic, a cork) and watch where they settle. Heavy objects sink through the light liquids but float on the denser ones.
- Tilt the jar gently and watch the layers shift but stay separate
- Try adding other liquids—maple syrup, milk, or corn syrup—and predict where they'll settle
What Kids Learn
This isn't just pretty (though it is pretty). Kids are learning:
- Density: Different substances have different weights
- Prediction: "Where will this new liquid go?"
- Observation: Watching carefully to see what actually happens
- Patience: Rushing ruins the layers—slow and steady wins
And here's the bonus: this experiment sits on your counter as a beautiful reminder that science is everywhere, even in the kitchen pantry.
Time needed: 10-15 minutes Mess factor: Low (as long as you pour carefully) Wow factor: High—everyone who sees it asks "How did you do that?"
Give it a try. You might just end up with a rainbow that teaches physics.
