Physics Basics

General Science · 6 min read · Sunitha Rao

Motion, force, energy and the SI units examiners keep asking about.

Physics questions in general studies papers stay close to definitions and units. Force is measured in newtons, work and energy in joules, power in watts, and pressure in pascals. A quick revision of units alone answers a surprising share of questions.

Newton's three laws describe inertia, the relation F = ma, and action-reaction pairs. Applications matter more than derivations: a passenger lurching forward when a bus brakes is inertia; a rocket rising is action-reaction.

Energy conservation ties the chapter together. Energy changes form - potential to kinetic, electrical to light - but the total remains constant in an isolated system.

Important points

  • SI unit of force is the newton; 1 N = 1 kg m/s^2.
  • Work is done only when a force produces displacement.
  • Power is the rate of doing work, measured in watts.
  • Speed of light in vacuum is about 3 x 10^8 m/s.
  • Energy can neither be created nor destroyed.

Key formulas

F = m x a

Work = Force x Displacement

Power = Work / Time

Examples

  1. A 10 kg mass accelerating at 2 m/s^2 needs F = ma = 20 N.
  2. Lifting 50 J of work in 10 s means a power of 5 W.

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