* Newton's Law of Universal Gravitation: The force of gravity between two objects is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.
* Symmetry: At the center of a spherically symmetric object, the gravitational forces from all the surrounding mass cancel out. Imagine yourself at the center: the mass pulling you to the left is perfectly balanced by the mass pulling you to the right, and so on for all directions.
* Shell Theorem: A mathematical proof known as the Shell Theorem states that the gravitational force inside a spherically symmetric shell of mass is zero. This applies to any spherical object, where you can think of its mass as being made up of concentric shells.
Important Note: This applies to the gravitational field *at* the center. The gravitational field *outside* the object is determined by the total mass of the object, as if all the mass were concentrated at its center.
