Question

Is Newton's law of universal gravitation valid only for particles? If yes, then how can we determine the gravitational force of interaction between two extended bodies? Between two spheres?

Answer 1

Newton's law of universal gravitation:

1. Newton's law of universal gravitation is not only valid for particles but also for terrestrial objects like planets, stars, etc.
2. Regular equation of Newton's law of universal gravitation is not applicable for extended objects.
3. They should have some specific equation depending on shape.
4. In spheres, mass is concentrated at the center. So, they are considered as point mass.