Summary Class 8 NCERT Explanation Easy Notes

Force and Laws Of Motion
Main Concepts
Force- Force is the push or pull made by an object which acts on
another object to change its position with respect to the amount of force.
For Example- While playing football we apply force on ball to bring it in
motion.
Newton’s First Law- It tells us that every object in this world is at rest
due to inertia (laziness of not moving) till any type of force acts on it and
changes its position.

10 Key Facts
 Mass = Measure of inertia
 Newton’s 2nd Law: F = m × a (Force = mass × acceleration)
 Newton’s 3rd Law: Every action has equal opposite reaction
 Momentum = mass × velocity (p = mv)
 Momentum conserved in collisions (no external force)
 1 Newton = 1 kg × 1 m/s²
 Inertia of motion (running stops hard)
 Inertia of direction (turning bus leans)
 Rocket = Action (gas down) Reaction (rocket up)
 Brakes = Friction stops wheels (inertia fights)

6 Exam MCQs
1. F = ? (a) ma ✓ (b) mv
2. Object resists change: (a) force (b) inertia ✓
3. Rocket works by: (a) 1st law (b) 3rd law ✓
4. Momentum unit: (a) Ns ✓ (b) kg
5. Action = -Reaction: (a) 2nd law (b) 3rd law ✓
6. Heavy object more: (a) inertia ✓ (b) speed

Quick Revision
 Newton’s Laws Trick: 1st(Lazy) 2nd(F=ma) 3rd(Action↑
Reaction↓)
 Momentum: p=mv (crash = big change)
 Exam Numerical: F=2kg×3m/s²=6N (5 marks)