  Supernova (SN) explosions are a major feedback mechanism regulating star
formation in galaxies through their momentum input. We review the observations
of SNRs in radiative stages in the Milky Way to validate the theoretical
results on the momentum/energy injection from a single SN explosion. For seven
SNRs where we can observe fast-expanding, atomic radiative shells, we show that
the shell momentum inferred from HI 21 cm line observations is in the range of
(0.5--4.5)$\times 10^5$ $M_\odot$ km s$^{-1}$. In two SNRs (W44 and IC 443),
shocked molecular gas with momentum comparable to that of the atomic SNR shells
has been also observed. We compare the momentum and kinetic/thermal energy of
these seven SNRs with the results from 1D and 3D numerical simulations. The
observation-based momentum and kinetic energy agree well with the expected
momentum/energy input from an SN explosion of $\sim 10^{51}$ erg. It is much
more difficult to use data/model comparisons of thermal energy to constrain the
initial explosion energy, however, due to rapid cooling and complex physics at
the hot/cool interface in radiative SNRs. We discuss the observational and
theoretical uncertainties of these global parameters and explosion energy
estimates for SNRs in complex environments.
