Laws of Motion
NIOS · Class 12 · Physics
Complete topic list for Laws of Motion in NIOS Class 12 Physics. Key concepts, sub-topics, and what to focus on for board exams.
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See them allTopics in Laws of Motion
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.
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.
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.
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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Central concept: Laws of Motion
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