  A liquid drop impacting a rigid substrate undergoes deformation and spreading
due to normal reaction forces, which are counteracted by surface tension. On a
non-wetting substrate, the drop subsequently retracts and takes off. Our recent
work (Zhang et al., \textit{Phys. Rev. Lett.}, vol. 129, 2022, 104501) revealed
two peaks in the temporal evolution of the normal force $F(t)$--one at impact
and another at jump-off. The second peak coincides with a Worthington jet
formation, which vanishes at high viscosities due to increased viscous
dissipation affecting flow focusing. In this article, using experiments, direct
numerical simulations, and scaling arguments, we characterize both the peak
amplitude $F_1$ at impact and the one at take off ($F_2$) and elucidate their
dependency on the control parameters: the Weber number $We$ (dimensionless
impact velocity) and the Ohnesorge number $Oh$ (dimensionless viscosity).
\VS{The first peak amplitude $F_1$ and the time $t_1$ to reach it depend on
inertial timescales for low viscosity liquids, remaining nearly constant for
viscosities up to 100 times that of water. For high viscosity liquids, we
balance the rate of change in kinetic energy with viscous dissipation to obtain
new scaling laws: $F_1/F_\rho \sim \sqrt{Oh}$ and $t_1/\tau_\rho \sim
1/\sqrt{Oh}$, where $F_\rho$ and $\tau_\rho$ are the inertial force and time
scales, respectively, which are consistent with our data.} The time $t_2$ at
which the amplitude $F_2$ appears is set by the inertio-capillary timescale
$\tau_\gamma$, independent of both the viscosity and the impact velocity of the
drop. However, these properties dictate the magnitude of this amplitude.
