The gravitational potential energy of two point masses m₁ and m₂ separated by distance r is (taking U = 0 at infinity)

1. Reference: U = 0 when the masses are infinitely far apart. 2. Since gravity is attractive, work is done BY the field when two masses come together. 3. So U(r) = −G m₁ m₂ / r (negative and finite as r decreases). 4. As r → 0, U → −∞; as r → ∞, U → 0. _Source: syllabus Physics, Ch 7 "Gravitation", §7.7_