CBSE · Class 9 · Science · Chapter 6

How Forces Affect Motion

Explore how forces change motion through inertia, momentum and the laws governing interactions between objects.

8 lessons 55 min
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Lessons in this chapter

  1. 1The Concept of ForceA force is not merely a push or pull; it is a directed interaction that can rewrite an object’s motion or shape.
  2. 2Balanced and Unbalanced ForcesSeveral forces can act together, but motion responds to their single combined result: the net force.
  3. 3The Force of Friction: Often Overlooked but Always PresentFriction is the quiet force that resists slipping, stops moving objects, and sometimes makes motion possible.
  4. 4Newton’s First Law of MotionObjects do not need a net force to keep moving; they need one only to change their velocity.
  5. 5Newton’s Second Law of MotionThe second law turns cause and response into a calculation linking net force, mass, and acceleration.
  6. 6Newton’s Third Law of MotionEvery force belongs to an interaction pair: equal and opposite, simultaneous, and acting on different objects.
  7. 7Forces Acting on a System of ObjectsChoosing a whole system can make internal force pairs disappear from the calculation and reveal the motion simply.
  8. 8Chapter Summary and PracticeThe chapter closes by connecting force diagrams, motion graphs, Newton’s laws, and system thinking into one problem-solving method.
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