The principle of conservation of momentum states that in any interaction between bodies, the total momentum before the interaction will equal the total momentum after the interaction, provided no external forces act upon the bodies
The force of attraction between any two point masses is directly proportional to the product of the masses, and inversely proportional to the square of the distance between them
The incident ray, the normal at the point of incidence, and the refracted ray are all in the same plane.
2. For any pair of media, the sin of i, the angle of incidence, is proportional to the sin of r, the angle of refraction, i.e. sin i/sin r = constant (Snell's law).