Lesson Plan

State Newton's law of universal gravitation and write its equation F = GmM/r²

Explain the gravitational constant G and distinguish it from the local acceleration due to gravity, g

Derive g = GM/r² and use it to explain why weight (not mass) varies from body to body

Perform calculations using F = GmM/r² and the orbital relation r³/T² = GM/4π²

Describe the Cavendish experiment and why measuring G was difficult

Explain Einstein's theory of general relativity at a conceptual level and contrast it with Newton's view of gravity

7.2

"Expressed in modern language, Newton's universal law of gravitation states that every object in the universe attracts every other object with a force that is directed along a line joining them. The force is directly proportional to the product of their masses and inversely proportional to the square of the distance between them." "G is a universal constant, meaning that it is thought to be the same everywhere in the universe. It has been measured experimentally to be G = 6.673 × 10⁻¹¹ N·m²/kg²." "Einstein based his theory on the postulate that acceleration and gravity have the same effect and cannot be distinguished from each other. He concluded that light must fall in both a gravitational field and in an accelerating reference frame." "To summarize the two views of gravity, Newton envisioned gravity as a tug of war along the line connecting any two objects in the universe. In contrast, Einstein envisioned gravity as a bending of space-time by mass."