Density Exploration Answer Key

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Date:

📚 Part 1: Understanding Density

1. What is the formula for calculating density?

Answer: Density = Mass ÷ Volume (D = m/V)

Teaching note: Emphasise units - g/cm³ or kg/m³

2. Which statement about density is correct?

Density depends on the size of an object

✓

Density is a property of the material itself

Larger objects always have higher density

Density changes with temperature (not always true)

Teaching note: Density is an intensive property - it doesn't change with amount of material.

3. A wooden block has a mass of 240g and a volume of 300cm³. Calculate its density.

Answer:

Density = Mass ÷ Volume

D = 240g ÷ 300cm³ = 0.8 g/cm³

Teaching note: Wood typically has density less than water (1.0 g/cm³), so it floats.

4. Which materials will float in water? (Density of water = 1.0 g/cm³)

✓

Cork (0.24 g/cm³)

Aluminium (2.7 g/cm³)

✓

Ice (0.92 g/cm³)

Steel (7.8 g/cm³)

Teaching note: Objects with density less than 1.0 g/cm³ will float in water.

🔬 Part 2: Density Applications

5. Explain why oil floats on water using the concept of density.

Answer: Oil has a lower density than water (approximately 0.8-0.9 g/cm³

compared to water's 1.0 g/cm³). Less dense liquids float on top of more

dense liquids due to buoyancy forces.

6. A metal cube has a volume of 50cm³ and a density of 8.9 g/cm³. What is its mass?

Answer:

Rearrange formula: Mass = Density × Volume

Mass = 8.9 g/cm³ × 50cm³ = 445g

Teaching note: This density suggests the metal is likely copper.

7. Why do ships made of steel float even though steel is denser than water?

Answer: Ships float because of their overall shape and design. The hull

contains large air spaces, making the average density of the entire ship

less than water. It's the total volume (steel + air) compared to total

mass that determines whether it floats.

8. Predict what happens when you mix honey (1.4 g/cm³), water (1.0 g/cm³), and cooking oil (0.9 g/cm³) in a container.

Answer: They will separate into layers with the least dense on top:

Top layer: Cooking oil (0.9 g/cm³)

Middle layer: Water (1.0 g/cm³), Bottom layer: Honey (1.4 g/cm³)

🎯 Part 3: Critical Thinking

9. A student measures the same rock's density three times and gets: 2.1 g/cm³, 2.8 g/cm³, and 2.2 g/cm³. What might explain these different results?

Possible answers: Measurement errors in mass or volume, trapped air

bubbles affecting volume measurement, using different measurement tools,

calculation errors, or the rock might have air pockets/different composition

throughout. Teaching note: Discuss experimental error and precision.

10. Design a simple experiment to compare the densities of three different liquids using household items.

Sample answer: Use a measuring cylinder to measure equal volumes

(e.g., 100mL) of each liquid. Use kitchen scales to measure the mass of

each volume. Calculate density for each using D = m/V. Alternatively,

pour all three liquids carefully into a tall container and observe which

layers form - denser liquids sink below less dense ones.

Density Exploration Answer Key

Density Exploration Answer Key

📚 Part 1: Understanding Density

🔬 Part 2: Density Applications

🎯 Part 3: Critical Thinking

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