Science lesson plan · 7th grade (Year 8 in England) · 45 minutes
Stretching springs: extension and Hooke's law
Forces and motion
CCSS NGSS.MS-PS2-2CCSS NGSS.HS-PS2-1England: KS3 Physics: Motion and forces (forces and elasticity)England: GCSE Combined Science: Forces (required practical: force and extension)
Objective and success criteria
Students will: Stretching springs: extension and Hooke's law.
- 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: Mass and weight (W = mg)
Leads to: Energy stored in a stretched spring (E = ½ k e²)
Materials: Force meters, Toy cars and ramps, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).
Warm-up · 5 min
- Quick retrieval from earlier learning (Mass and weight (W = mg)). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- What is the weight of a 8 kg object on Earth? Use g = 9.8 N/kg. → 78.4 NPrompt: weight = mass × gravitational field strength (W = m g)
- An astronaut's mass is 10 kg. Gravitational field strength on the Moon is 1.6 N/kg. What would their weight be there, in N? → 16 NPrompt: Mass stays the same everywhere; weight changes.
- Mass and weight: which statement is NOT true? (Mass and weight are the same thing. / Your mass is the same on the Moon as on Earth. / You would weigh less on the Moon than on Earth. / Weight is a force measured in newtons.) → Mass and weight are the same thing.Prompt: Which one changes on the Moon?
Hook · 5 min
- Drop a sheet of paper and a scrunched-up sheet together and ask why one falls faster.
- Share the objective: Stretching springs: extension and Hooke's law. 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 spring is 15 cm long. When a weight is hung on it, it is 17 cm long. What is the extension, in cm?
- Step 1: 17 − 15 = 2
- Step 2: So the answer is: 2 cm
- Answer: 2 cm
- 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 spring is 15 cm long. When a weight is hung on it, it is 21 cm long. What is the extension, in cm? → 6 cmPrompt: Extension is how much longer the spring has become.
- A spring has a spring constant of 200 N/m. What force is needed to stretch it by 8 cm, in N? (F = k × e, with e in metres) → 16 NPrompt: Convert the extension to metres first.
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 force of 2 N stretches a spring by 10 cm. What is the spring constant, in N/m? → 20 N/mPrompt: k = F ÷ e
- A spring is 12 cm long. When a weight is hung on it, it is 18 cm long. What is the extension, in cm? → 6 cmPrompt: Extension is how much longer the spring has become.
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: Mass and weight (W = mg).
- Use concrete materials: force meters.
- 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: Energy stored in a stretched spring (E = ½ k e²).
- 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-7.
Free lesson plan from eurekami.com/lesson-plan-builder