Class IX :: Chapter 10:: GRAVITATION
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- Universal Law of Gravitation: F = G × (m₁m₂)/r² ; G = 6.67×10⁻¹¹ N·m²/kg².
- Gravity & 'g': Acceleration due to gravity, g = GM/R² ≈ 9.8 m/s² on Earth's surface.
- Variation of 'g': g decreases with altitude (g' = gR²/(R+h)²) and depth (g' = g(1 – d/R)).
- Mass vs. Weight: Mass (kg) is scalar and constant; Weight (N) = m × g, varies with location.
- Weight on Moon: W_moon = (1/6) × W_earth because g_moon = g_earth/6.
- Free Fall: Motion under gravity alone; a = g (downward).
- Equations of Motion under Gravity: v = u ± gt, h = ut ± ½gt², v² = u² ± 2gh.
- Thrust & Pressure: Pressure = Thrust/Area ; SI unit = Pascal (Pa) = N/m².
- Buoyancy & Archimedes' Principle: Upthrust = Weight of fluid displaced.
- Floatation Condition: Object floats if its density ≤ fluid density.
- Relative Density: RD = Density of substance / Density of water (no unit).
- Kepler's Laws: Describe planetary motion; used by Newton to deduce inverse-square law.
Basic Level Questions
Chapter Summary
What You Will Learn: Chapter 10, "Gravitation," introduces you to one of the most fundamental forces in nature—gravity. You'll explore Newton's Universal Law of Gravitation, understand why objects fall with acceleration 'g', and learn to distinguish between mass and weight. The chapter also covers key fluid concepts like buoyancy, pressure, and Archimedes' principle, explaining why ships float and balloons rise.
Exam-Oriented Importance: This chapter is crucial for scoring in board exams and competitive tests like NTSE and Olympiads. It blends theory with numerical problems on gravitational force, free fall, weight variation, buoyancy, and pressure calculations. Mastering these concepts allows you to solve real-world physics problems and answer high-value questions confidently.
How This Website Helps: Our platform reinforces your learning with carefully graded MCQs—from basic definitions to challenging numerical problems. By practicing these questions, you can test your understanding of gravitational formulas, apply Archimedes' principle, and solve free-fall equations efficiently. This targeted practice builds speed, accuracy, and conceptual clarity, making you exam-ready and turning complex theory into easy marks.