PapaMarks
Library › Mechanics 1 WME01 › Newton's Second Law
AS Level · Mechanics 1 WME01

Newton's Second Law

Revise Newton's Second Law for Mechanics 1 WME01 (AS Level) — revision notes and instant AI marking.

📖 Revision notes · preview
Edexcel IAL · Mechanics 1

Newton's Second Law

Force equals mass times acceleration — but knowing how to apply it in every situation is what actually gets you marks.

5 Topics Practice Questions Included Concepts Checklist Exam Tips
Chapter Overview
The Big Idea
One sentence: When a resultant (net) force acts on a mass, it accelerates — and the relationship between them is always F = ma, whether the object is on a table, in a lift, or over a pulley.
F = ma

The core formula + how to combine with suvat

Ropes & Tow Bars

Tension, light strings, inextensible rods

Lifts

Reaction forces, vertical motion, apparent weight

Pulleys

Particles moving in different directions simultaneously

Vectors & F = ma

Forces as i-j vectors, magnitude, direction, equilibrium

Topic 1
F = ma — Newton's Second Law

Newton's Three Laws (Quick Reference)

First Law: An object stays at rest (or constant velocity) unless an unbalanced force acts on it. No net force → no acceleration.
Second Law: The resultant force on an object equals its mass multiplied by its acceleration. F = ma.
Third Law: For every action, there is an equal and opposite reaction — the force A exerts on B is equal in size but opposite in direction to the force B exerts on A.

The Formula — Explained

Fnet = m × a
F = resultant (net) force in Newtons (N)  |  m = mass in kilograms (kg)  |  a = acceleration in m s⁻²

The key word is resultant. You must add up all forces acting on an object (accounting for direction) before plugging into F = ma. A pushing force of 50 N and a friction force of 20 N in the opposite direction give a resultant of 30 N — that's the F in your equation.

Weight reminder: Weight is the force of gravity — W = mg where g = 9.8 m s⁻². Weight always acts vertically downwards. It's a force, not a mass!

Combining F = ma with Suvat

F = ma and the suvat equations are linked through acceleration. Here's when to use each:

Use F = ma when: you're given forces and/or mass, or asked to find a force or mass. Always gives you acceleration first.
Use suvat when: you have kinematic info (distance, speed, time) and no forces are mentioned. Suvat never involves mass or force directly.

In harder problems, use F = ma to find a, then substitute that a into a suvat equation to find distance or velocity.

Step-by-Step Method

  1. Draw a diagram. Label all forces, mark the positive direction. If a diagram is given, add to it. This step alone avoids most sign errors.
  2. Write F = ma (or suvat if no forces involved). If forces act in perpendicular directions, write a separate equation for each direction.
  3. Solve. In harder problems, simultaneous equations will appear — stay systematic.

Worked Example — Train Engine

A train engine of mass 5 tonnes moves with constant acceleration. In 8 s it travels 250 m and reaches a velocity of 35 m s⁻¹. The only driving force is 6250 N.

Practice Question 1
Topic 2
🔓 Read the full Newton's Second Law note → You're seeing the preview · sign in to read it all
Also in the full note
  • What Are Connected Particles?
  • Light Inextensible String — What It Means
  • Tow Bars — The Key Difference
  • Setting Up Equations — Two Approaches
  • Worked Example — Plane Towing Glider
  • What Makes Lift Problems Different?
  • The "Apparent Weight" Concept
  • Key Equations for Lift Problems
What's inside
📖 Revision notes 🎯 Learn mode ✦ AI flashcards ✓ Instant AI marking 🧊 3D explorers 🧪 Experiments & simulations 📈 Progress tracking
📄 Practise Newton's Second Law with Mechanics 1 WME01 past papers Every paper with its mark scheme — answer online, marked instantly. Open →

Read the full Newton's Second Law notes free

That's the preview — create a free account to read the rest, plus flashcards and practice questions with instant AI marking. No credit card.

Unlock the full notes free →

More Mechanics 1 topics

Quantities, Units & Modelling
Resolving Forces & Inclined Planes
suvat in 2D
Moments
Working with Vectors
Kinematics Graphs
Momentum & Impulse
F = ma
Forces
Velocity-Time Graphs