Chapter 6 — How Forces Affect Motion

Chapter 6 of NCERT Class 9 Science (Exploration, 2026-27 edition) explains how forces affect motion by covering Newton's three laws of motion, the concept of balanced and unbalanced forces, and the force of friction, with the SI unit of force being the newton (N).

Class 9 Science Chapter 6 'How Forces Affect Motion' from the NCERT Exploration textbook (2026-27) introduces the concept of force as a vector quantity measured in newtons (N). It explains balanced and unbalanced forces, and how friction opposes motion and depends on surface nature. Newton's First Law states that objects remain at rest or in uniform motion unless a net force acts on them. Newton's Second Law gives F = ma, meaning acceleration is proportional to net force and inversely proportional to mass. Newton's Third Law states that every action has an equal and opposite reaction, applicable to contact and non-contact forces alike.

1. 01Force is a vector quantity with both magnitude and direction; the SI unit is the newton (N), defined as the force producing 1 m/s² acceleration on a 1 kg mass.
2. 02Balanced forces are equal in magnitude and opposite in direction and produce no change in motion; unbalanced forces result in a net force that causes acceleration.
3. 03The force of friction acts opposite to the direction of motion and depends on the nature of surfaces in contact; smoother surfaces produce less friction and allow objects to travel farther.
4. 04Newton's First Law: an object at rest stays at rest and a moving object continues at constant velocity unless a net force acts on it.
5. 05Newton's Second Law: F = ma — net force equals mass times acceleration; acceleration increases with greater force and decreases with greater mass.
6. 06Newton's Third Law: whenever one object exerts a force on a second object, the second exerts an equal and opposite force on the first; this applies to all forces, including gravitational, magnetic, and electrostatic.