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Laws of Motion – Class 11 Physics NCERT | Newton’s Three Laws, Formulas & Derivations

🧲 Laws of Motion – Class 11 Physics (NCERT)

The Laws of Motion were given by Sir Isaac Newton and are fundamental to understanding force, motion, and mechanics in physics. This chapter from Class 11 NCERT explains how forces affect the motion of objects.

📘 Newton's First Law of Motion (Law of Inertia)

Statement: A body remains at rest or in uniform motion in a straight line unless acted upon by an external force.

🔹 This law defines inertia – the natural tendency of objects to resist change in their motion.

Inertia depends on mass. More mass → more inertia.

📌 Real-Life Example: You fall forward when a bus suddenly stops.

📘 Newton's Second Law of Motion

Statement: The rate of change of momentum of an object is directly proportional to the applied force and takes place in the direction of the force.

✅ Derivation:

  • Momentum, p = mv
  • Rate of change of momentum = d(mv)/dt = m dv/dt = ma (if mass is constant)
F = ma

📌 This is the most useful equation for calculating force, acceleration, or mass.

Units:

  • Force: Newton (N)
  • 1 N = 1 kg·m/s²

📘 Newton's Third Law of Motion

Statement: For every action, there is an equal and opposite reaction.

Faction = – Freaction

📌 Examples:

  • A gun recoils when a bullet is fired.
  • We walk forward by pushing backward on the ground.

📚 Summary Table: Newton’s Laws of Motion

Law Meaning Formula
1st Law Inertia – object stays at rest or constant motion unless acted upon —
2nd Law Force = rate of change of momentum F = ma
3rd Law Every action has an equal and opposite reaction F1 = –F2

⚠️ Important Notes:

  • Friction opposes motion and acts opposite to applied force.
  • Contact forces include tension, normal force, friction.
  • Non-contact forces include gravitational, magnetic, electric forces.

📈 Applications of Newton's Laws

  • Free body diagrams
  • Calculating net force on bodies
  • Solving pulley problems and block motion

Tags: Laws of Motion, Newton’s Laws, Class 11 Physics, CBSE, NCERT, JEE NEET Physics, Science Blog

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