Newton's Law of Universal Gravitation

Every object with mass in the universe attracts every other object with mass. This force of gravity is stronger for larger masses and weaker for objects that are farther apart. It follows an inverse square law, meaning if you double the distance, the force becomes four times weaker.

Formula: F = G(m₁m₂)/r²

Orbital Motion

An orbit is the path an object takes when it is 'falling' around a much larger object. It is a balance between the object's forward velocity (inertia) and the constant pull of gravity. Without gravity, the object would fly off in a straight line; without the forward velocity, it would fall directly into the central object.

Orbital Energy

An object in orbit has two kinds of energy. Kinetic Energy is the energy of its motion. Potential Energy is the stored energy it has due to its position in the gravitational field. The total energy of the orbit is the sum of these two.

Formula: E_total = KE + PE