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6th grade · Science · Unit 3 of 17

Density & Buoyancy

Mass, volume, floating and sinking

What your child practices

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.

Texas Essential Knowledge and Skills (TEKS) teks student expectation: 6.6(D) · comparing the density of substances in different fluids

How we explain it

Children can open this short lesson before they practice.

  1. Density = mass ÷ volume, often in g/cm³.
  2. Water's density is 1.00 g/cm³. Less dense things float on it; denser things sink.
  3. Cutting an object doesn't change its density.
  4. Liquids layer by density: the densest at the bottom.

Example: A block has a mass of 60 g and a volume of 50 cm³. Will it float in water? Density = 60 ÷ 50 = 1.2 g/cm³. 1.2 is more than water's 1.00, so it sinks. Answer: no, it sinks

Density & Buoyancy in Texas

In the Texas Essential Knowledge and Skills (TEKS), this is unit 3 of 17 in 6th grade Science, after The Periodic Table and before Chemical Reactions.

Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.

Source: Texas Education Agency (TEA)

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

    Pour these liquids into a tall jar. Order them from the bottom layer to the top layer.

    • 💧Water (1.00 g/cm³)
    • 🫒Vegetable oil (0.92 g/cm³)
    • ⚪Mercury (13.6 g/cm³)
    • 🍯Honey (1.42 g/cm³)

  2. Question 2

    A lake freezes from the top down. Which fact about density helps explain this?

    • Ice is denser than water, so it sinks.
    • Ice has no volume.
    • Cold water has no particles.
    • Ice is less dense than liquid water, so it stays at the top.

  3. Question 3

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

    • 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.
    • Only small objects sink.

  4. Question 4

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

    Sort into: 🛟 Floats · ⚓ Sinks

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

  5. Question 5

    A metal has a density of 3 g/cm³. What is the mass of 4 cm³ of it, in g?

    answer boxg

  6. Question 6

    Ice floats in liquid water. What does this tell you?

    • Ice is a gas.
    • Water particles do not move.
    • Ice is less dense than liquid water.
    • Ice has more mass than the same volume of water.

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