Gravity and Gravitation

Gravity is a force of attraction that exists between every pair of objects in the Universe. This force is proportional to the mass of each object in each pair, and inversely proportional to the square of the distance between the two; thus,

where m₁ is the mass of the first object, m₂ is the mass of the second object, r is the distance between their centers, and G is a fixed number termed the gravitational constant. (If m₁ and m₂ are given in kilograms and r in meters, then G = 6.673 × 10^-11N m²/kg².)