Year 9 Science · Unit 3 · Lesson 2

Law of Conservation of Energy

Challenge Worksheet

Name

Date

Class

Learning Goals

Explain the law of conservation of energy to a younger audience
Use conservation reasoning to prove perpetual motion is impossible
Connect scientific principles to real-world engineering claims

Go Deeper

Challenge 8 marks

Explain it to a Year 7 student

Imagine a Year 7 student asks you: "Why is a perpetual motion machine impossible?" Use the sentence starters below to build a clear explanation using what you know about conservation of energy. You can use real examples from everyday life.

Starter 1: "The basic idea of conservation of energy is…"

Starter 2: "A perpetual motion machine would need to… but this is impossible because…"

Starter 3: "In every real machine, some energy always becomes… This means that over time…"

Starter 4: "A good everyday example that shows why perpetual motion is impossible is…"

Show What You Know

1. In 2023, an inventor claimed to have built a machine that produces more electricity than it consumes, a so-called "over-unity" device. Evaluate this claim using the law of conservation of energy. What would you expect to find if you tested this machine carefully?

Challenge 3 marks

2. A pendulum swings back and forth. Each swing is slightly lower than the last. Construct a detailed energy argument to explain this observation. In your answer, identify the system, describe all energy transformations, and explain why the pendulum does not violate conservation of energy even as it loses height.

Challenge 4 marks

Wrap Up

In one sentence, what was the main idea of this lesson?