Three-Layer Float

Objectives

• Predict, test and explain the relative densities of common liquids.

Materials

• Per Demo:
  1 tall, clear cup
  3 liquids of different densities (choose from): honey, corn syrup, dish soap, water with a drop of food colouring, vegetable oil, food colouring

Key Questions

• Which liquid is densest?
• How can you tell?

What To Do

1. Show students the three liquids and ask them to predict which liquid has the highest density and which liquid has the lowest density.
2. Can students predict what will happen when they pour the three liquids into the cup?
3. Ask students to, one at a time, pour each of the liquids into the cup. Watch the denser liquids sink to the bottom.

Teacher Tips 
Pour each layer slowly, because mixing can make it more difficult to see the intended result. Start with the densest liquid, then add liquids with lower densities. Tilt the cup and pour onto the side of the cup to cause the least disturbance to the liquids.

Extensions

• This experiment can easily be extended to any number of different layers, as long as the liquids used are immiscible (i.e., do not mix). We can see this happen with other fluids, like gases, too.
• Show students a cork, a coin and a grape. Have them to predict which item will float in which layer.
• Predict and investigate the relative density of cream and milk - Students often expect cream to be denser because it is thicker!
• How does this phenomenon explain how a hot air balloon works?