Science lesson plan · 8th grade (Year 9 in England) · 45 minutes
Conservation of energy and wasted energy
Energy
CCSS NGSS.MS-PS3-5CCSS NGSS.HS-PS3-1England: KS3 Physics: Energy (changes in systems)England: KS4 Combined Science: Energy
Objective and success criteria
Students will: Conservation of energy and wasted energy.
- 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: How devices transfer energy
Leads to: Kinetic and gravitational potential energy; Efficiency; Use energy conservation to find speeds and heights
Materials: Wind-up toys or a pendulum, Energy transfer 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 (How devices transfer energy). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- What is the main useful energy output of an electric kettle? (light / sound / heating (thermal) / movement (kinetic)) → heating (thermal)Prompt: What is the device for?
- A battery-powered torch (flashlight) is switched on. Which list shows the energy transfer? (light → chemical → sound / sound → light / chemical → electrical → light (and some heat) / kinetic → nuclear → light) → chemical → electrical → light (and some heat)Prompt: Start with the energy store in the battery.
- Which device is mainly designed to give out heating (thermal)? (a traffic light / an electric toy car / an electric kettle / a torch (flashlight)) → an electric kettlePrompt: Think about what you use each device for.
Hook · 5 min
- Wind up a toy or stretch an elastic band and ask where the energy goes.
- Share the objective: Conservation of energy and wasted energy. 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 speaker is supplied with 200 J of energy. It transfers 80 J usefully. How much energy is wasted, in J?
- Step 1: 200 − 80 = 120
- Step 2: So the answer is: 120 J
- Answer: 120 J
- 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 speaker is supplied with 200 J of energy. It transfers 40 J usefully. How much energy is wasted, in J? → 160 JPrompt: Energy is conserved: input = useful output + wasted output.
- How can wasted energy in a machine with moving parts be reduced? (make it move faster / remove the oil / lubricate the parts to reduce friction / paint it a darker colour) → lubricate the parts to reduce frictionPrompt: What causes heating where parts rub?
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.
- What does the law of conservation of energy say? (Energy cannot be created or destroyed, only transferred / Energy is used up and disappears / Energy is always destroyed as heat / Machines create energy) → Energy cannot be created or destroyed, only transferredPrompt: Where does "used" energy go?
- A speaker is supplied with 2000 J of energy. It transfers 1800 J usefully. How much energy is wasted, in J? → 200 JPrompt: Energy is conserved: input = useful output + wasted output.
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: How devices transfer energy.
- Use concrete materials: wind-up toys or a pendulum.
- 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: Kinetic and gravitational potential energy; Efficiency; Use energy conservation to find speeds and heights.
- 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