1. Observations In life
   1. An apple falls from a tree.
   2. The Moon orbits Earth.
2. Newton's Law of Gravitation
   1. Sir Isaac Newton was the first scientist to precisely define the gravitational force, and to show that it could explain both falling bodies and astronomical motions.
   2. The law states that every particle of matter in the universe attracts every other particle with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
   3. The direction of the force is along the line joining the line of particles.
   4. Gravitational force is always attractive.
3. Equation
   1. Considering masses in kilograms and distance in meters.