Force and Laws of Motion
Newton's three laws, inertia, momentum, and force.
Chapter Overview
Newton's three laws explain how forces change motion. Topics include inertia, momentum, impulse, force-mass-acceleration relation, and conservation of momentum in collisions.
Newton's Laws
First law
Body remains at rest or uniform motion unless acted by unbalanced force (inertia)
Second law
F = ma ; F = Δp/Δt
Third law
Every action has equal and opposite reaction
Momentum
p = mv (kg·m/s)
Conservation of Momentum
- In isolated system, total momentum before = after collision
- m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂
- Rocket propulsion uses third law
Solved Examples
Step-by-step solutions — read each step before checking the final answer.
F = ma
2 kg mass accelerated at 3 m/s². Find force.
- 1F = ma = 2 × 3
Answer
6 N
Momentum conservation
2 kg ball at 3 m/s hits 1 kg stationary ball; they stick. Final velocity?
- 1m₁u₁+m₂u₂=(m₁+m₂)v
- 26+0=3v
- 3v=2 m/s
Answer
2 m/s
Key Points to Remember
- ✓ Inertia ∝ mass
- ✓ Impulse = FΔt = Δp
- ✓ Friction opposes relative motion
Exam Tips
- • Draw free-body diagrams
- • State Newton's laws in words before applying
- • Check sign convention for direction
Practice MCQs — Force and Laws of Motion
Test your understanding with topic-wise multiple choice questions. Explanations appear after each answer.
SI unit of force is: