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Laws of Motion — Revision Notes

NIOS · Class 12 · Physics

Laws of Motion revision notes for NIOS Class 12 Physics: 4 topics in quick points. Part of the NIOS Class 12 Physics syllabus.

44 questions35 flashcards13 formulas & key relations5 concepts

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Illustrations demonstrating the three types of inertia: inertia of rest, inertia of motion, and inertia of direction, using common real-world scenarios.
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Key Topics to Revise

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1. Concept of Inertia and Force

  • Inertia is the natural tendency of a body to resist any change in its state of rest or uniform motion in a straight line.
  • Mass is the measure of inertia – a heavier body has more inertia and is harder to accelerate or decelerate.
  • Force is a vector quantity that can change the shape, size, speed, or direction of motion of a body.
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2. Newton's First Law of Motion

  • Statement: A body continues to remain in its state of rest or of uniform motion in a straight line unless acted upon by a net external (unbalanced) force.
  • This law is also called the Law of Inertia.
  • It defines force qualitatively – force is that which changes the state of motion.
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3. Linear Momentum and Newton's Second Law

  • Linear Momentum (p) = mass × velocity. It is a vector quantity with direction same as velocity.
  • SI unit of momentum: kg m/s or N·s
  • Newton's Second Law: The rate of change of momentum of a body is directly proportional to the net external force acting on it, and the change occurs in the direction of the force.
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4. Newton's Third Law and Conservation of Momentum

  • Newton's Third Law: When two bodies interact, force exerted by body A on body B is equal in magnitude and opposite in direction to force exerted by B on A. F₁₂ = -F₂₁
  • Action and reaction forces are ALWAYS equal in magnitude, opposite in direction, and act on DIFFERENT bodies – they never cancel each other.
  • Common examples: (a) Rocket propulsion – gases pushed back, rocket moves forward. (b) Swimming – hand pushes water back, body moves forward. (c) Recoil of gun – bullet moves forward, gun kicks back. (

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Full Notes

Key Concepts

Inertia is the natural tendencyLinear momentum (p) of a bodyNewton's Second Law statesNewton's Third Law statesIn an ISOLATED SYSTEM (no external

Frequently Asked Questions

What are the important topics in Laws of Motion for NIOS Class 12 Physics?
Key topics in Laws of Motion include Concept of Inertia and Force, Newton's First Law of Motion, Linear Momentum and Newton's Second Law, Newton's Third Law and Conservation of Momentum. Study these first, then practise questions on each for the NIOS Class 12 board exam.
How should I revise Laws of Motion for the NIOS Class 12 board exam?
Learn the core ideas first, then work through the 44 practice questions on Laws of Motion. Revise definitions regularly and use flashcards for quick recall before the exam.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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