Physics Basics for RRB NTPC: Motion, Force, Energy, Light and Electricity
A from-scratch, Class 10 level guide to the physics every RRB NTPC aspirant needs: motion and its equations, Newton's laws of force, work-energy-power, and the basics of light and electricity - with SI units, a worked train example, and a quick-revision table.
By the PadhoDost Team · 📖 8 min read · Updated 4 August 2026
Part of Railway Exams (RRB) prep🧠 The local train jerk
You are standing in a Mumbai local. The moment the train jerks forward, your body tumbles backward. Nobody pushed you, right? Your body simply wanted to STAY where it was while the train suddenly moved ahead. That single everyday moment hides three big ideas of physics: motion, inertia and force. Master these basics, dost, and this whole RRB syllabus starts feeling like a familiar train route.
Motion: how things move
Motion means a change in an object's position with time. To describe it we use a few key words. Distance is the total path length covered (a scalar - only size, unit metre, m). Displacement is the shortest straight-line gap from start to finish, WITH direction (a vector, unit m). Speed is distance per unit time (scalar, m/s). Velocity is displacement per unit time - speed with a direction (vector, m/s). Acceleration is the rate of change of velocity, measured in metre per second squared (m/s squared). A scalar has only magnitude; a vector has magnitude AND direction - this difference is a favourite exam trap.
📝 A train leaving the platform
A train starts from rest and accelerates at a = 2 m/s squared for t = 10 s. Find its final velocity and the distance covered.
Given: u = 0 (starts from rest), a = 2 m/s squared, t = 10 s.
Final velocity: v = u + at = 0 + (2 x 10) = 20 m/s.
Distance: s = ut + (1/2)at squared = 0 + (1/2)(2)(10 x 10) = 100 m.
Answer: after 10 seconds the train is moving at 20 m/s and has covered 100 m.
Force and Newton's three laws
A force is a push or pull that can change an object's speed, direction or shape. Its SI unit is the newton (N), where 1 N = 1 kg x m/s squared. Newton gave three laws. First law (law of inertia): a body stays at rest or in uniform motion in a straight line unless an external force acts on it - this is why you fell back in the train. Second law: force equals mass times acceleration (F = ma); for the same acceleration, a heavier body needs more force. Third law: for every action there is an equal and opposite reaction - a rocket pushes gas downward and is thrown upward. Momentum, p = mv (unit kg x m/s), measures the 'quantity of motion'.
Work, energy and power
In physics, work is done only when a force makes an object move along the direction of the force. Just holding a heavy bag while standing still does zero work! Energy is the capacity to do work; the two common types are kinetic energy (energy of motion) and potential energy (energy of position, like water stored high up in a dam). Power is how FAST work is done. Work and energy share the same unit - the joule (J) - while power is measured in watt (W).
Light and electricity
Light travels in a straight line and, in vacuum, at about 3 x 10 to the power 8 m/s - the fastest speed in nature. When light bounces off a surface it is reflection (the angle of incidence equals the angle of reflection). When it bends on passing from one medium into another, like a straw looking broken in a glass of water, it is refraction. Electricity is the flow of charge. Current (I) is measured in ampere (A), potential difference or voltage (V) in volt (V), and resistance (R) in ohm. Ohm's law links them: V = I x R. Electric power is P = V x I, and household energy is billed in kilowatt-hour (kWh), the 'unit' on your bijli bill.
| Quantity | SI unit | Formula / note |
|---|---|---|
| Force | newton (N) | F = ma |
| Work / Energy | joule (J) | W = F x d |
| Power | watt (W) | P = W / t |
| Speed / Velocity | metre/second (m/s) | distance or displacement / time |
| Acceleration | m/s squared | change in velocity / time |
| Electric current | ampere (A) | I = V / R |
| Resistance | ohm | R = V / I |
Quick revision before the exam
- ✓Scalars have size only (distance, speed, mass); vectors have size and direction (displacement, velocity, force).
- ✓Equations of motion (constant a): v = u + at, s = ut + (1/2)at squared, v squared = u squared + 2as (s is displacement).
- ✓Newton: 1st law = inertia, 2nd law F = ma, 3rd law equal and opposite reaction.
- ✓Work and energy are both in joule; power is in watt (1 W = 1 J/s).
- ✓g = 9.8 m/s squared; speed of light in vacuum is about 3 x 10 to the power 8 m/s.
- ✓Ohm's law: V = IR; electric power P = VI; bijli bill unit = kilowatt-hour (kWh).
⚡ Quick check
A moving bus suddenly applies its brakes and the passengers lean forward. Which idea explains this best?
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