Grade 9 · ⚛️ Physics · Matter and its properties
Build a density tower in a glass
Stack honey, water and cooking oil in one glass and watch them refuse to mix. Then drop in small objects and see where each one floats.
Why this matters
When the Awash floods, oil and fuel spilled upstream spread as a thin film on top of the water — never underneath. Fishermen on Lake Tana know that a wooden boat floats while an iron anchor sinks. Both come down to one idea: density. Engineers use it to design ships, separate crude oil and even test whether honey from the market has been watered down.
Watch the demo
Video coming soon
We're recording a demo for this experiment. Until then, follow the step-by-step guide below.
The science
What is density?
Density is how much mass is packed into a given volume: ρ = m / V. Units are g/cm³ or kg/m³. Water has a density of about 1 g/cm³.
Floating and sinking
A liquid or object that is less dense than the liquid around it rises and floats. One that is more dense sinks. Liquids that don't mix settle into layers, densest at the bottom.
You'll need
- A tall clear glass or bottle
- Honey↳ Thick sugar syrup works too
- Water with a few drops of food colouring↳ A little tea or coffee also colours it
- Cooking oil
- Small test objects: a grape, a cork or bottle cap, a coin, a piece of pasta or a dried bean
- A spoon
Safety first
- Wipe up spills right away — oil and honey make floors slippery.
- Don't drink the mixture afterwards.
Step by step
0/5 doneWhat you should see
Three clear layers form: honey at the bottom, water in the middle, oil on top. The coin sinks to the bottom. A grape or bean usually rests between water and honey, and a cork floats on the oil.
Why it happens
Honey is denser than water (about 1.4 g/cm³), and oil is less dense (about 0.9 g/cm³), so they sort themselves by density. Each object stops at the layer where the liquid above it is less dense than the object, and the liquid below it is more dense.
Didn't work? Try this
The water and honey mixed into one cloudy layer.
You poured too fast. Start again and pour the water very slowly down the back of a spoon held against the glass.
I can't see the line between water and oil.
Add more food colouring (or tea) to the water so it contrasts with the yellow oil.
Still stuck? Ask the lab assistant
Check your understanding
1. Oil floats on water. What does this tell you?
2. A 20 g object has a volume of 10 cm³. Will it sink or float in water (1 g/cm³)?
Your lab notebook
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