Quick Physics Chapter 10 Gravitation Notes | CBSE Class 9

1. Mastering Gravitation — Class 9 Physics Notes That Win Marks Introduction Gravitation is one of those chapters in Class 9 Science that builds the foundation for so many key ideas — motion, orbits, weight, free fall. But understanding it well isn’t just about reading: it’s about applying and connecting ideas. Here are study tips & essential points from the “Gravitation” notes that can help you score higher. Why Gravitation Matters •It explains everyday things — why things fall, why planets orbit, why we stay grounded. •It introduces important physics concepts like force, acceleration, inverse-square laws, centres of mass, etc. These show up again & again in higher classes. Key Concepts & Definitions 1. Gravitation / Gravity The concept of Gravitation has a universal approach; on the contrary, Gravity is specifically the effect of the Earth’s gravitational pull. 2. Universal Law of Gravitation Newton’s law: Every two masses attract each other with a force that is - directly proportional to the product of their masses, - inversely proportional to the square of the distance between their centers. Formula: ? = ??? ?2 where G is the universal gravitational constant. 3. Free Fall Understand free fall: only gravity acts, and acceleration is constant = g. Recognize that heavier objects don’t fall “faster” when air resistance is ignored. 4. Gravitational Constant (G) •Value: approximately 6.673 × 10−11??2/??2 5. Mass vs Weight •Mass = the amount of matter in an object (constant everywhere).

2. •Weight = gravitational force acting on that mass; depends on g, so weight varies with location. Formula: W=m.g 6. Acceleration due to Gravity (g) How to derive g for Earth’s surface using the universal law (with Earth’s mass and radius). Recognize that g changes slightly depending on altitude, latitude, etc. Study Tips to Get Better Marks •Include diagrams and units: Always draw the two-masses with separation r, arrows showing gravitational force, labelling masses, distances. Mark units of G, g, etc. Diagrams help fetch marks. •Derivations / proofs: Be able to derive formula for g from universal gravitation law, etc. Show steps. •List assumptions: When using formulas, clarify assumptions: e.g., ignoring air resistance, treating Earth as spherical, etc. •Examples & numerical problems: Practice problems about weight on moon, calculating force between masses, comparing forces when distance changes, etc. These often come in exams. •Comparative tables: For frequently confused terms like mass vs weight, or G vs g — a small table helps clarity. •Relate to real-life situations: Questions like “Why do we feel lighter at top of tall building?”, “Why are astronauts weightless?”, etc., are liked in exams. •Revision schedules: Revisit this chapter after a few days; try solving NCERT and sample papers. •Answer writing: Use precise definitions, include formulae, use correct units, label diagrams, write steps in problem solving clearly.