Year 7 Science · Unit 3 · Lesson 6
Challenge Worksheet
Learning Goals
What if…?
Scenario
A new electric car (Car E) is being compared to a standard petrol car (Car P) of the same model. Car E's electric motor produces twice the torque (force) of Car P's petrol engine. However, Car E is 1.5 times heavier than Car P because of its large battery pack. Both cars start from rest and are given full throttle on a straight road. A journalist claims: "The electric car must be faster because it has twice the force."
Using what you know from Newton's Second Law qualitatively, predict and explain what would actually happen to Car E's acceleration compared to Car P. Is the journalist's claim fully correct? Use scientific terms in your answer.
Extension: Hint to check your thinking
If force doubles (×2) but mass also increases (×1.5), think about what happens to the ratio of force to mass. Does the electric car still have a bigger "push per kilogram" than the petrol car? Show your reasoning in words — no formula required.
1. A rocket burns fuel as it launches. As the fuel burns, the rocket's mass decreases while the thrust (force) from the engines stays roughly constant. Using Newton's Second Law qualitatively, explain what happens to the rocket's acceleration as it rises through the atmosphere. Why does the rocket accelerate faster as the launch progresses?
2. Two students disagree: Student A says "more force always means an object goes faster." Student B says "more force means the object accelerates more — not necessarily that it goes faster." Who is correct, and why? Give an example to support the correct student's position.
Wrap Up
In one sentence, what was the main idea of this lesson?