Which formula can be used to express the law of conservation of momentum, where p = momentum?

In the midst of building hostilities, Washington decided to resign from office after his second term. On September 19, 1796, the American Daily Advertiser published Washington's Farewell Address to the nation. The basic premise of the address was a condemnation of political parties. Washington warned that the development of parties would destroy the government, and worried that special interest groups and foreign nations would easily dominate the factions. On this note, he implored future generations to avoid embroilment in the affairs of other nations, and concentrate on the development of "efficient government" at home, free from foreign influence. Washington left office in March 1797, leaving the nation still very much divided.