Physics Class 9 Chapter 4 - Turning Effect of Force

Who was the first man to come up the idea of gravity? Find the gravitational force of attraction between two spheres each of mass 1000 kg. The distance between the centres of the spheres is 0.5 m? What is the force called with which everybody attracts every other body in this earth? Which law of Newton states that: “Everybody in universe attracts every other body with force which is directly proportional to product of their masses and inversely proportional to square of distance between their centres”?