Science lesson plan · 8th grade (Year 9 in England) · 45 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 · 5 min
- Quick retrieval from earlier learning (Density). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- A block has a mass of 135 g and a volume of 50 cm³. What is its density, in g/cm³? → 2.7 g/cm³Prompt: density = mass ÷ volume
- 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.
- A block has a mass of 22.6 g and a volume of 2 cm³. What is its density, in g/cm³? → 11.3 g/cm³Prompt: density = mass ÷ volume
Hook · 5 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 · 10 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 · 10 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- A measuring cylinder contains 75 cm³ of water. When a stone is lowered in, the level rises to 95 cm³. What is the volume of the stone, in cm³? → 20 cm³Prompt: The stone pushes aside (displaces) its own volume of water.
- A copper object has a mass of 71.2 g. Lowered into 30 cm³ of water, it raises the level to 38 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 · 10 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 8 questions are on the student sheet below, with answers in the key.
Exit ticket · 5 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- A material has a density of 0.5 g/cm³. What is this in kg/m³? (1 g/cm³ = 1000 kg/m³) → 500 kg/m³Prompt: Multiply by 1000.
- A glass object has a mass of 12.5 g. Lowered into 50 cm³ of water, it raises the level to 55 cm³. What is its density, in g/cm³? → 2.5 g/cm³Prompt: Find the volume from the change in water level.
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