Overview

Classical Mechanics (Newtonian Mechanics) is the physics of the everyday world. It describes how things move, from apples falling to planets orbiting. It ruled physics for 200 years until Quantum Mechanics and Relativity came along.

Core Idea

The core idea is determinism. If you know the position and velocity of every particle in the universe, and the forces acting on them, you can predict the future perfectly (Laplace’s Demon).

Formal Definition

Based on Newton’s Laws of Motion:

  1. Inertia: Objects keep doing what they’re doing unless acted on by a force.
  2. F=ma: Force equals mass times acceleration.
  3. Action-Reaction: For every action, there is an equal and opposite reaction.

Intuition

It’s the billiard ball model of the universe. Things are solid, distinct, and move in predictable paths.

  • Kinematics: Describing motion (velocity, acceleration).
  • Dynamics: Explaining motion (forces, torques).

Examples

  • Projectile Motion: Calculating the path of a cannonball (a parabola).
  • Orbital Mechanics: How satellites stay in space (balancing gravity and forward velocity).
  • Conservation Laws: Energy and Momentum are never lost, just transferred.

Common Misconceptions

  • Misconception: Heavier objects fall faster.
    • Correction: Galileo showed that in a vacuum, a feather and a hammer fall at the same rate. Air resistance is what slows the feather down.
  • Misconception: You need force to keep moving.
    • Correction: You only need force to change motion (acceleration). In space, you coast forever.
  • Lagrangian Mechanics: An alternative formulation using energy (Least Action Principle) instead of forces.
  • Chaos Theory: Even deterministic systems can be unpredictable if they are sensitive to initial conditions.
  • Engineering: Applied classical mechanics.

Applications

  • Civil Engineering: Building bridges that don’t fall down (Statics).
  • Rocket Science: Getting to the moon.
  • Sports: Analyzing the spin of a baseball.

Criticism and Limitations

  • Scale: It fails at the very small (Quantum Mechanics) and the very fast/heavy (Relativity).

Further Reading

  • The Feynman Lectures on Physics, Vol. 1 by Richard Feynman
  • Classical Mechanics by John R. Taylor