A density tower looks like magic the first time you see it: four or five liquids in one glass, each staying in its own colorful band instead of mixing together. But the trick is real science. Each liquid has its own density, so the heaviest liquids sink and the lighter ones float above them.
What you need
- A tall clear glass or jar
- Honey or corn syrup
- Dish soap
- Water
- Vegetable oil
- Food colouring
- A spoon or turkey baster
- Optional: a grape, raisin, bead, or small piece of pasta to test where objects settle
Safety note: This is not a drinking experiment. Once the liquids are mixed, do not taste them.
Steps
- Put honey in the bottom of the glass first.
- Slowly pour dish soap down the inside wall of the glass so it lands gently on top of the honey.
- In a separate cup, mix a few drops of food colouring into water. Pour it in slowly.
- Add vegetable oil last, very gently.
- Wait a minute and watch the layers settle into bands.
Tip: Pouring too fast makes the liquids mix. Slow pouring is part of the experiment.
Predict first
Before you pour, try ranking the liquids from most dense to least dense. Then compare your prediction with the final tower.
Typical order from bottom to top:
- Honey — about 1.4 g/cm³
- Dish soap — about 1.06 g/cm³
- Water — about 1.00 g/cm³
- Vegetable oil — about 0.92 g/cm³
What’s happening?
Density tells you how much mass is packed into a certain volume. The formula is:
density = mass / volume
where:
- density is how tightly packed the matter is
- mass is how much matter there is
- volume is how much space it takes up
If two liquids do not mix easily, the denser one sinks below the less dense one. Gravity pulls on both, but the denser liquid packs more mass into the same space, so it settles lower.
That is why:
- honey sinks below dish soap
- dish soap sinks below water
- water sinks below oil
Oil and water also stay apart because they are made of different kinds of molecules. Water is polar and oil is non-polar, so they do not mix well even when you stir them.
Try the object test
Drop a small object into the tower:
- A grape often sinks through the oil and water, then stops near the dish soap or honey.
- A raisin may stop higher up.
- A small plastic bead may float near the top.
The object sinks until it reaches a layer dense enough to support it. That is the same idea behind boats floating and submarines diving.
Key vocabulary
- Density — how much mass is packed into a given volume
- Mass — how much matter is in an object
- Volume — how much space an object or liquid takes up
- Polar — a molecule with uneven charge; water is polar
- Non-polar — a molecule without uneven charge; oil is non-polar
- Miscible — able to mix completely; water and oil are not miscible
Math connections
Suppose you pour 50 ml of each liquid into the glass.
- Total volume of the tower: 50 + 50 + 50 + 50 = 200 ml
- Fraction of the tower that is oil: 50/200 = 1/4
- Fraction that is water plus oil together: 100/200 = 1/2
If one liquid layer is twice as tall as another, is that because it is more dense? Not necessarily. Height depends on how much volume you poured in. Density decides the order of the layers, not how thick each layer looks.
Try more
- Add rubbing alcohol if you have it with an adult helping and predict where it will settle.
- Try warm water versus cold water. Does temperature change the layering?
- Draw your tower and label each layer from least dense to most dense.