Newton's laws of motion — CIE A-Level Physics
CIE A-Level Physics · 9702 · 15 min read
1. Newton's First Law of Motion ★★☆☆☆ ⏱ 5 min
Exam tip: Always confirm both speed AND direction are constant before concluding net force is zero
2. Newton's Second Law of Motion ★★★☆☆ ⏱ 7 min
3. Newton's Third Law of Motion ★★★☆☆ ⏱ 6 min
Exam tip: Always mention that action-reaction forces are the same type and act on different bodies in your exam answers.
Common Pitfalls
Why: Action-reaction pairs act on two different bodies, while balanced forces both act on the same body
Why: $F=ma$ only holds for constant mass; the general form of Newton's second law uses rate of change of momentum
Why: Newton's second law requires the sum of all forces, not just the single applied force you are given
Why: Examiners require you to state all three laws separately when asked, and the first law defines inertial reference frames
Quick Reference Cheatsheet