Newton's Laws of Motion

Introduction

  • Presented by Sir Isaac Newton in 1686
  • Published in "Philosophiæ Naturalis Principia Mathematica"

1. Newton'sFirst Law of Motion

Statement

An object maintains its state of rest or uniform motion in the absence of external forces.

Key Points

  • Objects at rest remain at rest without external forces
  • Objects in motion continue moving at constant velocity without external forces
  • Introduces concept of inertia: resistance to change in motion
  • Mass is a measure of inertia

Mathematical Expression

If F = 0, then ΔV = 0

Applications

  • Passengers' motion in vehicles
  • Objects in space

2. Newton'sSecond Law of Motion

Statement

The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.

Key Points

  • Relates force, mass, and acceleration
  • Greater force results in greater acceleration
  • Greater mass results in less acceleration for the same force

Mathematical Expression

F = ma

SI Unit of Force

  • Newton (N)
  • 1 N = 1 kg·m/s²

3. Newton'sThird Law of Motion

Statement

For every action, there is an equal and opposite reaction.

Key Points

  • Forces always occur in pairs
  • Action and reaction forces are equal in magnitude but opposite in direction
  • Act on different objects

Mathematical Expression

F = -F

Examples

  • Jumping
  • Rocket propulsion
  • Punching or kicking objects

Limitations of Newton's Laws

  1. Not applicable at atomic scale (quantum mechanics applies)
  2. Not accurate for objects moving at speeds close to light speed (relativistic mechanics applies)
  3. Provide good approximations for macroscopic scale and practical energies/forces