Lecture
This lecture covers the concepts of gravitational, electric, and magnetic forces, starting with the Cavendish experiment to measure the Earth's mass. It then compares gravitational and electric forces, discussing the forces exerted by charges and the forces at a distance. The lecture also explains the forces of contact, focusing on the behavior of objects near the Earth's surface and the interaction between charges. It concludes with a detailed explanation of the forces exerted by a spring, including its natural length and rigidity. Throughout the lecture, various examples and comparisons are provided to illustrate the different types of forces.