Math lesson plan · 8th grade (Year 9 in England) · 45 minutes
Volume of a cone
Geometry
CCSS 8.G.C.9England: KS3 Geometry and measuresEngland: GCSE Foundation Geometry and measures
Objective and success criteria
Students will: Volume of a cone.
- 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: Volume of a cylinder
Leads to: Find a missing radius or height from a volume
Materials: Rulers and protractors, Squared or dotted paper, Shape cut-outs, Mini whiteboards and pens, Printed student sheet (below).
Warm-up · 5 min
- Quick retrieval from earlier learning (Volume of a cylinder). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- A cylinder has radius 2 cm and height 20 cm. Find its volume in cm³, to 1 decimal place. → 251.3Prompt: A cylinder is a prism with a circular cross-section.
- A cylinder has radius 3 m and height 13 m. Its volume is kπ m³. What is k? → 117Prompt: V = πr²h. Leave π as a symbol.
- A water bottle is a cylinder 12 cm across and 15 cm tall. How many litres does it hold? (1 litre = 1000 cm³.) Round to 2 decimal places. → 1.7Prompt: Radius = 12 ÷ 2.
Hook · 5 min
- Show a photo of a building, a tile pattern or a road sign and ask what shapes and angles students can spot.
- Share the objective: Volume of a cone. 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 cone has radius 7 cm and height 18 cm. Its volume is kπ cm³. What is k?
- Step 1: ⅓ × 49 × 18 = 294
- Step 2: 294π cm³
- Answer: 294
- 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 cone has radius 4 cm and height 12 cm. Its volume is kπ cm³. What is k? → 64Prompt: V = ⅓πr²h.
- An ice-cream cone has radius 7 cm and height 13 cm. Find its volume in cm³, to 1 decimal place. → 667.1Prompt: Use V = ⅓ × π × r² × h.
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 cylinder and a cone have the same radius and height. The cylinder holds 84 ml. Maya says the cone holds 42 ml. How much does the cone really hold, in ml? → 28Prompt: Compare V = πr²h and V = ⅓πr²h.
- A cone has radius 8 cm and height 6 cm. Its volume is kπ cm³. What is k? → 128Prompt: V = ⅓πr²h.
Watch out for
- Thinking a square turned on its corner is no longer a square.
- Reading the wrong scale on a protractor.
Support and stretch
Support
- Review first: Volume of a cylinder.
- Use concrete materials: rulers and protractors.
- Give the first step of each question, or a partly worked example to finish.
- Pair with a confident partner for the guided practice.
Stretch
- Move on to: Find a missing radius or height from a volume.
- 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/math/grade-8.
Free lesson plan from eurekami.com/lesson-plan-builder