  A classic lift decomposition (von K\'arm\'an & Sears 1938) is conducted on
potential flow simulations of a near-ground pitching hydrofoil. It is
discovered that previously observed stable and unstable equilibrium altitudes
are generated by a balance between positive wake-induced lift and negative
quasi-steady lift while the added mass lift doesn't play a role. Using both
simulations and experiments, detailed analyses of each lift component's
near-ground behavior provide further physical insights. When applied to
three-dimensional pitching hydrofoils the lift decomposition reveals that the
disappearance of equilibrium altitudes for AR < 1.5 occurs due to the magnitude
of the quasi-steady lift outweighing the magnitude of the wake-induced lift at
all ground distances. Scaling laws for the quasi-steady lift, wake-induced lift
and the stable equilibrium altitude are discovered. A simple scaling law for
the lift of a steady foil in ground effect is derived. This scaling shows that
both circulation enhancement and the velocity induced at a foil's leading edge
by the bound vortex of its ground image foil are the essential physics to
understand steady ground effect. The scaling laws for unsteady pitching foils
can predict the equilibrium altitude to within 20% of its value when St < 0.45.
For St equal to or greater than 0.45 there is a wake instability effect, not
accounted for in the scaling relations, that significantly alters the
wake-induced lift. These results not only provide key physical insights and
scaling laws for steady and unsteady ground effect, but also for two schooling
hydrofoils in a side-by-side formation with an out-of-phase synchronization.
