Universal Gravitational Constant:A constant value denoted by G that appears in the equation for calculating gravitational force. It has a value of approximately 6.674 × 10^-11 N(m/kg)^2.
Inverse Square Law: The relationship between distance and intensity where as you move further away from an object, the intensity decreases proportionally to the square of the distance.
Newton's Third Law:Also known as the law of action-reaction, it states that for every action force, there is an equal and opposite reaction force.