Gravitation — Simple Notes with Solved Examples

GRAVITATION — QUICK NOTES 1. Universal Law of Gravitation Every object attracts every other object with a force that is: - directly proportional to the product of their masses, and - inversely proportional to the square of the distance between them. F = G · (m1 · m2) / r² Here G = 6.674 × 10⁻¹¹ N·m²/kg² (the universal gravitational constant). 2. Free Fall When an object falls only under gravity, its acceleration is g ≈ 9.8 m/s². g does not depend on the mass of the falling object — a stone and a feather fall at the same rate in a vacuum. 3. Mass vs Weight - Mass (m): the amount of matter in a body. Same everywhere. Unit: kg. - Weight (W): the force of gravity on the body, W = m · g. Changes with g. Unit: newton (N). SOLVED EXAMPLE A body of mass 5 kg is placed on the Earth's surface. Find its weight. W = m · g = 5 × 9.8 = 49 N. TRY IT YOURSELF 1. Why does a coin and a paper reach the ground together in a vacuum tube? 2. What is your weight (in N) if your mass is 40 kg?