Answer

The Moon's gravity exerts a differential (tidal) force across Earth's diameter — the side of Earth nearest the Moon is pulled more strongly than Earth's center, and Earth's center is pulled more strongly than the far side. This differential stretches Earth's oceans into a prolate spheroid shape, creating two tidal bulges: one on the side facing the Moon (direct gravitational pull) and one on the opposite side (where the Moon's pull is weakest relative to Earth's center, effectively leaving water 'behind' due to inertia and the centrifugal effect of the Earth-Moon barycentric orbit). As Earth rotates once every ~24 hours beneath these two relatively fixed bulges, most locations pass through both bulges, producing roughly two high tides and two low tides per day — a pattern called semidiurnal tides. The Sun also contributes a tidal force (about 46% as strong as the Moon's), producing spring tides (reinforced) at new and full moon and neap tides (diminished) at quarter phases. The actual timing and height of tides are also shaped by coastal geometry, ocean basin resonance, and the Moon's elliptical orbit (perigean tides). A nuanced answer distinguishes between the common misconception that the far-side bulge is caused purely by centrifugal force versus the more accurate differential gravity (tidal force) explanation in a non-rotating reference frame.