Density: Floating and Sinking

Active learning builds understanding because density is a concept best grasped through hands-on experience. When students predict and test objects, they connect abstract ideas to concrete evidence. This approach helps them move beyond guesswork to confident explanations about why things float or sink.

• 2nd Class
• Young Explorers: Investigating Our World
• 4 activities
• 30 min–45 min

Learning Objectives

1. Classify objects as either floating or sinking in water based on experimental results.
2. Explain the relationship between an object's density and its ability to float or sink in water.
3. Design a fair test to determine if an irregularly shaped object will float or sink.
4. Predict whether common objects will float or sink based on their observed properties and prior knowledge.

Inquiry Circle

⏱ 30 min·Pairs

Prediction Chart: Sink or Float

List 10 classroom objects on a chart. In pairs, students predict if each will sink or float, then test in a water tub and record results with drawings or ticks. Discuss surprises as a class.

Prepare & details

Analyze the relationship between mass, volume, and density.

Facilitation Tip: During the Prediction Chart activity, circulate with guiding questions like, 'What do you notice about the objects that might affect their density?' to encourage deeper thinking.

Setup: Groups at tables with access to source materials

Materials: Source material collection, Inquiry cycle worksheet, Question generation protocol, Findings presentation template

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Inquiry Circle

⏱ 45 min·Small Groups

Clay Boat Challenge

Give each small group modeling clay. Students form a ball that sinks, then reshape it into a boat that floats by trapping air. Measure and compare mass to explain results.

Prepare & details

Predict whether an object will float or sink based on its density relative to water.

Facilitation Tip: For the Clay Boat Challenge, remind students to focus on changing shape, not mass, to see how volume affects floating.

Setup: Groups at tables with access to source materials

Materials: Source material collection, Inquiry cycle worksheet, Question generation protocol, Findings presentation template

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Inquiry Circle

⏱ 35 min·Whole Class

Density Column Layers

Pour liquids of different densities like oil, water, and syrup into clear cylinders. Students drop small objects like a grape or cork into the column and observe where they settle. Predict positions first.

Prepare & details

Design an experiment to determine the density of an irregularly shaped object.

Facilitation Tip: When building Density Column Layers, model precise pouring to prevent mixing and ensure clear layers of liquids.

Setup: Groups at tables with access to source materials

Materials: Source material collection, Inquiry cycle worksheet, Question generation protocol, Findings presentation template

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Inquiry Circle

⏱ 40 min·Small Groups

Volume by Displacement

Use a measuring cylinder with water. Students drop irregular objects like pebbles, mark water rise, and calculate volume. Compare to mass for density predictions.

Prepare & details

Analyze the relationship between mass, volume, and density.

Facilitation Tip: During the Volume by Displacement activity, demonstrate how to read the water level carefully to avoid inaccuracies.

Setup: Groups at tables with access to source materials

Materials: Source material collection, Inquiry cycle worksheet, Question generation protocol, Findings presentation template

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Teaching This Topic

Start with familiar examples, like why boats float despite their weight, to build curiosity. Use guided questions to help students connect density to buoyancy. Avoid rushing to explanations; let their observations shape the discussion. Research shows that students learn best when they test ideas, make mistakes, and revise their thinking based on evidence.

What to Expect

Students will confidently use the term 'density' when predicting and explaining outcomes. They will recognize that weight alone does not determine floating or sinking. Clear evidence from their experiments helps them articulate patterns and correct misconceptions.

Watch Out for These Misconceptions

Common Misconception

During the Prediction Chart activity, watch for students who assume heavy objects always sink and light ones float.

What to Teach Instead

Use the Prediction Chart to test objects of equal volume but different masses, like a steel washer and a plastic button, to show that density determines the outcome.

Common Misconception

During the Clay Boat Challenge, students may think the shape alone decides if it floats.

What to Teach Instead

Have students reshape the same piece of clay into different forms and observe how air pockets or volume changes affect floating, then relate this to density.

Common Misconception

During the Density Column Layers activity, students might believe all wooden objects float.

What to Teach Instead

Include wood samples of different densities in the column to show that some types sink, reinforcing that density, not material alone, matters.

Assessment Ideas

Exit Ticket

After the Prediction Chart activity, give each student a small card. Ask them to draw one object that sinks and one that floats, and write one sentence explaining why using the word 'density'.

Discussion Prompt

After the Clay Boat Challenge, present a large floating object (like a piece of wood) and a small sinking object (like a pebble). Ask: 'Why does the big piece of wood float while the tiny pebble sinks? How does density help us understand this?'

Quick Check

During the Volume by Displacement activity, ask students to hold up fingers to indicate their prediction: 1 finger for 'sink', 2 fingers for 'float'. After placing the object in water, ask them to explain their prediction using 'density'.

Extensions & Scaffolding

• Challenge students to design a boat using only one sheet of aluminum foil that can hold the most pennies without sinking.
• For students who struggle, provide pre-cut shapes of clay to test and compare, focusing on volume changes.
• Deeper exploration: Have students research and explain how submarines use density to control their depth in water.

Key Vocabulary

Density	Density is a measure of how much mass is packed into a certain volume. It tells us how 'heavy' something is for its size.
Float	An object floats when it stays on the surface of a liquid, like water, without sinking.
Sink	An object sinks when it falls to the bottom of a liquid, like water.
Mass	Mass is the amount of 'stuff' or matter in an object. It is often measured using a balance scale.
Volume	Volume is the amount of space an object takes up. For liquids, it can be measured in containers with markings.