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Grade 8 · Science · Unit 3 of 9

Density & Buoyancy

Mass, volume, floating and sinking

What your child practises

Calculating density from mass and volume, explaining why solids, liquids and gases differ in density using the particle theory, and predicting whether objects float or sink in different fluids.

Saskatchewan Curriculum outcome: FD8.1, FD8.2 · density, buoyancy and forces in fluids

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    Water has a density of 1.00 g/cm³. Does each material float or sink in water?

    Sort into: 🛟 Floats · ⚓ Sinks

    • 🧊ice (0.92 g/cm³)
    • 🔩iron (7.9 g/cm³)
    • 🎣lead (11.3 g/cm³)
    • 🪙copper (8.9 g/cm³)
    • 🍾cork (0.24 g/cm³)
    • 🫒vegetable oil (0.92 g/cm³)
    • 🥫aluminum (2.7 g/cm³)
    • 🪵pine wood (0.5 g/cm³)
    Show answer

    🛟 Floats: ice (0.92 g/cm³), cork (0.24 g/cm³), vegetable oil (0.92 g/cm³), pine wood (0.5 g/cm³) · ⚓ Sinks: iron (7.9 g/cm³), lead (11.3 g/cm³), copper (8.9 g/cm³), aluminum (2.7 g/cm³)

    Hint: A material floats if its density is less than 1.00 g/cm³ and sinks if it is greater.

  2. Question 2

    A sample of a liquid has a density of 3 g/mL and a mass of 9 g. What is its volume in mL?

    answer boxmL

    Show answer

    3 mL

    Hint: Volume = mass ÷ density.

  3. Question 3

    Vegetable oil floats on water. Which has the greater density?

    • Neither has density.
    • They are the same.
    • water
    • vegetable oil
    Show answer

    water

    Hint: The less dense liquid floats on top of the denser one.

  4. Question 4

    Two cubes have the same volume. Cube A has a mass of 100 g and cube B has a mass of 200 g. Which is denser?

    • They have the same density.
    • It cannot be known.
    • cube B
    • cube A
    Show answer

    cube B

    Hint: With equal volumes, the greater mass means the greater density.

  5. Question 5

    A metal has a density of 3 g/cm³. What is the mass of 9 cm³ of it, in g?

    answer boxg

    Show answer

    27 g

    Hint: Mass = density × volume.

  6. Question 6

    A large steel ship floats even though steel is denser than water. Why?

    • Only small objects sink.
    • Steel becomes lighter in water.
    • The hull encloses a lot of air, so the ship's overall density is less than water's.
    • The engines hold the ship up.
    Show answer

    The hull encloses a lot of air, so the ship's overall density is less than water's.

    Hint: Overall density includes all the air inside the hull.

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