Density Tower in a Jar

You will need

• Tall clear glass or jarAt least 10 inches (25 cm) tall preferred; a pint jar works
• Honey or corn syrupAbout 3 tablespoons (45 ml)
• Dish soapAbout 3 tablespoons (45 ml); blue or green color helps visibility
• WaterAbout 3 tablespoons (45 ml)
• Vegetable oilAbout 3 tablespoons (45 ml)
• Small cups or glassesOne per liquid, for pre-measured pouring
• Food coloringoptionalOne drop in the water only to distinguish it; stains skin

  Food coloring stains skin and counters — use just one drop and wipe spills immediately.

• FlashlightoptionalShine from below to illuminate the layers

Steps

1. 1

   Pre-pour each liquid

   Measure each liquid into its own small cup before the child arrives. Line them up in pouring order: honey or corn syrup first, then dish soap, then water, then oil last. If you are adding food coloring, stir one drop into the water cup now.

2. 2

   Explain the question

   Set the empty jar in front of the child and say, 'These four liquids all look kind of the same, but they weigh different amounts. I wonder if we can stack them on top of each other without stirring.' Let the child predict whether that is possible.

3. 3

   Pour the first layer

   Show the child how to tilt the jar slightly and pour the honey slowly down the inside wall rather than splashing it straight down. Pour the honey together the first time so the child sees the technique, then let them take over for the next layers.

   Tip: Go slowly — thirty seconds per layer is about right for keeping the layers distinct.

4. 4

   Add each layer in turn

   Have the child pour each liquid in order, pausing after each to watch the new liquid settle. Ask 'Where did it stop? Why do you think it stopped there?' before adding the next one. Resist the urge to rush through — the pauses are where the thinking happens.

5. 5

   Observe and count the layers

   Once all four liquids are in, set the jar on a flat surface and step back. Count the visible layers together. If you have a flashlight, shine it from below and watch the layers glow. Ask the child to describe the order from bottom to top.

6. 6

   Test an object

   Drop a small item into the jar — a raisin, a small button, or a grape — and watch where it stops sinking. Ask the child to predict before it goes in. This extends the activity naturally and introduces the idea that solids have density too.

   Tip: A grape tends to rest between the oil and water layers, which surprises most children.

Take it to the table

Materials checklist, the steps and the variations on one Letter page.