Science activity
Density Tower Rainbow
Make a rainbow in a jar! Pour different liquids into a tall glass and watch them stack on top of each other. Some liquids are heavier and sink to the bottom!
Materials and setup
- tall clear glass or jar
- honey
- corn syrup
- dish soap
- food coloring
- vegetable oil
- water
- rubbing alcohol
- small objects (grape, cork, penny, bead)
- kitchen scale
How this changes by age
Pre-K (ages 3–4)
Make a rainbow in a jar! Pour different liquids into a tall glass and watch them stack on top of each other. Some liquids are heavier and sink to the bottom!
Steps
- Gather 3-4 liquids: honey, dish soap (colored), water (add food coloring), and vegetable oil.
- Slowly pour honey into a tall clear glass first. Then carefully add dish soap on top.
- Gently pour colored water down the side of the glass. Then add oil on top.
- Look at your rainbow tower! 'The heavy liquids sank to the bottom and the light ones floated on top!'
- Drop small objects in: a grape, a cherry tomato, a cork. Where does each one float?
- Tell a grown-up one thing that surprised you.
Learning objectives
- Observe that different liquids have different weights and layer naturally
- Understand that heavier liquids sink below lighter ones
- Predict where small objects will float in a density column
Kindergarten (ages 5–6)
Build a density tower with 5 liquids and test which objects float at each level. Make predictions before testing and record your results!
Steps
- Gather 5 liquids: honey, corn syrup, maple syrup or milk, water (colored with food coloring), and vegetable oil.
- Predict: 'Which liquid do you think is heaviest? Which is lightest?' Draw your prediction.
- Carefully pour each liquid into a tall clear container, starting with the one you think is heaviest.
- Wait for layers to settle. Did your prediction match? Draw the actual result.
- Test 8 small objects: raisin, grape, cherry tomato, plastic bead, cork, penny, button, popcorn kernel. Predict where each will float, then drop it in.
- Record results in a chart: object name, prediction (which layer), and actual result (which layer).
- Tell a grown-up one thing that surprised you.
Learning objectives
- Build a density column and understand liquid layering
- Make and test predictions about where objects will float
- Record experimental predictions and results in an organized chart
Early elementary (ages 6–8)
Investigate density scientifically: build a 7-layer density tower, calculate the density of liquids and solid objects, and explain why density determines layering and floating.
Steps
- Research density: density = mass / volume. Denser substances sink below less dense ones.
- Build a 7-layer tower: honey, corn syrup, maple syrup, whole milk, water, vegetable oil, rubbing alcohol. Add food coloring to clear liquids for visibility.
- Measure the density of each liquid: weigh a known volume (e.g., 50 mL) on a kitchen scale. Calculate density in g/mL. Record in a data table.
- Test 10 solid objects: first calculate each object's density (weigh it, then measure volume by water displacement). Predict which layer it will float at based on its density.
- Drop each object in and compare results to your predictions. Were your density calculations accurate?
- Write a report explaining: What is density? Why do liquids layer by density? How can you predict where a solid object will float? Include your data table and calculations.
- In one sentence, tell a parent or sibling what surprised you today.
Learning objectives
- Calculate density using mass and volume measurements
- Build a multi-layer density column and explain the layering principle
- Predict floating positions of objects based on calculated density values
Upper elementary (ages 8–10)
Conduct a comprehensive density investigation: precisely measure liquid and solid densities, explore how temperature and dissolved substances affect density, and connect density concepts to real-world phenomena.
Steps
- Build a precision density tower with 8+ layers. Measure each liquid's density to two decimal places using a graduated cylinder and scale. Create an ordered data table.
- Investigate temperature and density: measure the density of water at different temperatures (cold from fridge, room temp, warm from tap). Graph temperature vs. density. Explain the anomaly: liquid water is densest at about 4 degrees C. When it freezes, hydrogen bonds lock the molecules into an open hexagonal structure that is LESS dense than liquid water — which is why ice floats. Most substances get denser as they solidify; water is unusual.
- Investigate dissolved substances: measure the density of plain water vs. salt water at different concentrations (1 tsp, 2 tsp, 4 tsp per cup). How does dissolved salt change density? This explains why it is easier to float in the ocean!
- Calculate the density of 10 irregular objects using water displacement. Compare measured density to known values to identify mystery materials (is it aluminum, steel, wood, or plastic?).
- Research real-world density: how do submarines control buoyancy? Why do hot air balloons rise? How do lava lamps work? Explain each using density principles.
- Write a scientific paper: present all density measurements, graphs of temperature and concentration effects, mystery material identifications, and real-world applications.
- In one sentence, tell a parent or sibling what surprised you today.
Learning objectives
- Measure density with precision and understand significant figures
- Analyze how temperature and dissolved substances affect liquid density
- Apply density concepts to explain real-world phenomena like ocean buoyancy and hot air balloons
Safety and evidence note
Read the full activity before beginning. An adult should supervise tools, heat, food, outdoor work, movement, and experiments as appropriate. Completion records that the activity was done; the child’s explanation, work sample, photo, or demonstration is stronger evidence of learning than a completion check alone.
Related science activities
Animal Body Language & Behavior
Animals talk all the time — they just don't use words. A dog wags its tail high and loose when it is happy, but tucks its tail between its legs when it is scared. A cat holds its tail straight up like a pole to say hello, but puffs it up like a bottle brush when it is startled. A bird sings soft songs on a calm morning, but makes a sharp 'chip-chip-chip' alarm call when something dangerous is near. If you watch closely, you can understand exactly what they are feeling.
Animal Habitat Diorama
Choose a favorite animal and build its home in a shoebox! Use natural materials, paper, and toy animals to create a habitat scene.
Animal Habitats & Needs
Here is an animal that will surprise you: the mantis shrimp can punch with the force of a bullet. It sees 16 types of color — humans only see 3. And it lives in a burrow it digs itself at the bottom of the ocean. When scientists first discovered how powerful the mantis shrimp's punch was, it shattered the equipment they were using to measure it. Every animal's body is perfectly matched to the place it lives. Today you'll discover how that matching works.
Animal Tracks & Signs
Look for clues that animals have been nearby! Find footprints, nests, holes, or chewed leaves.