Relativistic laws of motion and E = mc^2^

Special Relativity and Electrodynamics (Spring, 2012)

April 23, 2012

Professor Susskind begins with a review of space- and time-like intervals, and explains how these intervals relate to causality and action at a distance. He then introduces space-time four-vectors and four-velocity in particular.

After presenting these concepts, Professor Susskind introduces relativistic particle mechanics. He presents the action principle for a particle in free space, and derives the Lagrangian for such a particle.

Building on these concepts, Professor Susskind derives the relativistic formulas for momentum and energy, and discusses relativistic mass, and how the conservation of momentum and energy are modified by relativity. He then shows the origin of Einstein's famous equation E = mc2.

The lecture concludes with a discussion of massless particles under relativity.

  • Relativistic particle mechanics
  • More space-like and time-like intervals
  • Four-vectors and four-velocity
  • Relativistic action and Lagrangian for the motion of a particle
  • Relativistic momentum and energy
  • Derivation of mass-energy equivalence: E = mc^2^
  • Massless particles