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Science lesson plan · 8th grade (Year 9 in England) · 30 minutes

Find density using water displacement

States of matter

CCSS NGSS.MS-PS1-2CCSS NGSS.SEP 3England: KS3 Physics: Matter (density)England: GCSE Combined Science: Particle model of matter (required practical: density)

Objective and success criteria

Students will: Find density using water displacement.

  • I can answer questions on today's skill on my own, without help.
  • I can explain each step and say why it works.
  • I can check my answer and spot a mistake.

Before and after

Needs first: Density

Leads to: the next skill in this area.

Materials: Ice, water and a kettle (teacher demo), Particle diagrams, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).

Warm-up · 4 min

  • Quick retrieval from earlier learning (Density). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. A block has a mass of 56.5 g and a volume of 5 cm³. What is its density, in g/cm³? → 11.3 g/cm³Prompt: density = mass ÷ volume
  2. The density of ice is 0.92 g/cm³. Water's density is 1.0 g/cm³. Does a solid piece of ice float or sink in water? (floats / sinks) → floatsPrompt: Compare the density with water's density.
  3. A block has a mass of 8 g and a volume of 2 cm³. What is its density, in g/cm³? → 4 g/cm³Prompt: density = mass ÷ volume

Hook · 3 min

  • Show an ice cube melting and a kettle steaming and ask what is the same and what is different.
  • Share the objective: Find density using water displacement. Read the success criteria together.

I do: model it · 7 min

  • Work through the example out loud, saying why you do each step, not just what you do.
  • Example: A measuring cylinder contains 50 cm³ of water. When a stone is lowered in, the level rises to 62 cm³. What is the volume of the stone, in cm³?
  • Step 1: 62 − 50 = 12
  • Step 2: So the answer is: 12 cm³
  • Answer: 12 cm³
  • Pause after each step and ask a student to say what comes next.

We do: guided practice · 6 min

  • Do these together. Students try each step on whiteboards before you reveal it.
  • Use the hints as prompts rather than giving the answer.
  1. A measuring cylinder contains 50 cm³ of water. When a stone is lowered in, the level rises to 55 cm³. What is the volume of the stone, in cm³? → 5 cm³Prompt: The stone pushes aside (displaces) its own volume of water.
  2. A copper object has a mass of 44.5 g. Lowered into 60 cm³ of water, it raises the level to 65 cm³. What is its density, in g/cm³? → 8.9 g/cm³Prompt: Find the volume from the change in water level.

You do: independent practice · 7 min

  • Students work on the student sheet. Circulate and check the first two answers of every student early.
  • Students who finish: write a question of their own for a partner, with the answer.

The 6 questions are on the student sheet below, with answers in the key.

Exit ticket · 3 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. A measuring cylinder contains 75 cm³ of water. When a stone is lowered in, the level rises to 83 cm³. What is the volume of the stone, in cm³? → 8 cm³Prompt: The stone pushes aside (displaces) its own volume of water.
  2. An object has a density of 11.3 g/cm³. Water has a density of 1 g/cm³. Will the object float or sink in water? (it floats / it sinks) → it sinksPrompt: Compare the object's density with water's.

Watch out for

  • Everyday meanings of words getting in the way of the science meaning: define key words explicitly.
  • Remembering facts without the reason: ask "why?" and "what is the evidence?"

Support and stretch

Support

  • Review first: Density.
  • Use concrete materials: ice, water and a kettle (teacher demo).
  • Give the first step of each question, or a partly worked example to finish.
  • Pair with a confident partner for the guided practice.

Stretch

  • Explain a common mistake in writing and how to fix it.
  • Write a word problem that uses today's skill, then solve a partner's.

Homework and more practice

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-8.

Free lesson plan from eurekami.com/lesson-plan-builder

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Find density using water displacement

Name

Date

Score/ 6

  1. Question 1

    An object has a density of 0.5 g/cm³. Water has a density of 1 g/cm³. Will the object float or sink in water?

    • A. it floats
    • B. it sinks

  2. Question 2

    A measuring cylinder contains 75 cm³ of water. When a stone is lowered in, the level rises to 87 cm³. What is the volume of the stone, in cm³?

    Answercm³

  3. Question 3

    A granite object has a mass of 13.5 g. Lowered into 30 cm³ of water, it raises the level to 35 cm³. What is its density, in g/cm³?

    Answerg/cm³

  4. Question 4

    A material has a density of 0.92 g/cm³. What is this in kg/m³? (1 g/cm³ = 1000 kg/m³)

    Answerkg/m³

  5. Question 5

    A measuring cylinder contains 50 cm³ of water. When a stone is lowered in, the level rises to 58 cm³. What is the volume of the stone, in cm³?

    Answercm³

  6. Question 6

    A copper object has a mass of 106.8 g. Lowered into 50 cm³ of water, it raises the level to 62 cm³. What is its density, in g/cm³?

    Answerg/cm³

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Answer key: Find density using water displacement

  1. 1. A. it floats

  2. 2. 12 cm³

  3. 3. 2.7 g/cm³

  4. 4. 920 kg/m³

  5. 5. 8 cm³

  6. 6. 8.9 g/cm³