  A microeconomic model is developed, which accurately predicts the shape of
personal income distribution (PID) in the United States and the evolution of
the shape over time. The underlying concept is borrowed from geo-mechanics and
thus can be considered as mechanics of income distribution. The model allows
the resolution of empirical and definitional problems associated with personal
income measurements. It also serves as a firm fundament for definitions of
income inequality as secondary derivatives from personal income distribution.
It is found that in relative terms the PID in the US has not been changing
since 1947. Effectively, the Gini coefficient has been almost constant during
the last 60 years, as reported by the Census Bureau.
