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Physics / Classical Mechanics
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Classical Mechanics

The physics of objects large enough to see and slow enough to feel — how things move, why they move, and what stays conserved while they do. Built on foundations laid by Newton in 1687 and reformulated by Lagrange and Hamilton over the following two centuries.

Classical mechanics is the branch of physics describing the motion of macroscopic bodies under the action of forces, using the framework established by Newton's three laws of motion and extended by the energy, momentum, and analytical formulations developed through the 18th and 19th centuries.

What this domain covers

Classical mechanics answers a small number of questions with enormous reach: given the forces acting on an object, how will it move? Given how several objects move, what is conserved when they interact? It covers kinematics (the description of motion without reference to its cause), dynamics (motion as a consequence of force, built on Newton's three laws), the energy and momentum conservation laws that follow from Newton's laws, rotational motion, gravitation, oscillatory motion, and the more abstract Lagrangian and Hamiltonian reformulations that underlie much of modern theoretical physics, including quantum mechanics.

Classical mechanics is not "wrong" or "replaced" by relativity or quantum mechanics — it is their low-velocity, macroscopic limit, accurate to extraordinary precision anywhere speeds are far below the speed of light and objects are far larger than atoms. GPS satellites, bridges, rockets, and every everyday collision are calculated using classical mechanics.

Kinematics

Kinematics describes motion — position, velocity, acceleration — without asking what causes it. It is the geometric skeleton that dynamics later fills with force and mass.

Common mistakeVelocity and speed are not the same thing. Velocity is a vector — it has direction. Speed is only its magnitude. A car going around a circular track at constant speed has constantly changing velocity, because direction is changing.

Newton's Laws

Three statements, published in the Principia Mathematica in 1687, that define what force does to motion and remain the operating axioms of classical dynamics.

Work, Energy & Power

Energy conservation is the single most useful problem-solving principle in classical mechanics — often faster than applying Newton's laws directly.

Momentum & Collisions

Rotational Motion

Gravitation

Simple Harmonic Motion

Lagrangian & Hamiltonian Mechanics

A reformulation of mechanics around energy rather than force, developed by Lagrange (1788) and Hamilton (1833). This is the version of classical mechanics that generalises directly into quantum mechanics.

Fluid Mechanics

Sources

  • Newton, I. (1687). Philosophiæ Naturalis Principia Mathematica. London: Royal Society. Public domain.
  • Goldstein, H., Poole, C., Safko, J. (2002). Classical Mechanics, 3rd ed. Addison Wesley. Chapters 1–2, 8.
  • Feynman, R.P., Leighton, R.B., Sands, M. The Feynman Lectures on Physics, Vol. I, Chapters 1–10. feynmanlectures.caltech.edu
Last verified: July 2026 · Source: Newton (1687); Goldstein et al. (2002) · Confidence: high

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