Tides
Tides are gravity's difference, not its strength. The Moon pulls on the whole Earth, but it pulls the near side a little harder than the centre, and the centre a little harder than the far side — because gravity weakens with distance. Subtract the pull on the centre (which the entire planet shares as it falls around the Moon) and what remains is the tidal force, stretching Earth along the line to the Moon.[1]
The orange arrows are the tidal force — what's left of the Moon's gravity after removing the pull on the planet's centre. They point outward at both endsof the planet–Moon line and inward at the sides, squeezing the oceans into two bulges (near and far). As the planet spins under them (watch the white dot), any coast passes through both bulges each rotation — two high tides a day. Bring the Moon closer and the effect, which falls off as 1/distance³, grows fast. When the Sun lines up with the Moon their bulges add (spring tides); at right angles they partly cancel (neap tides).
That stretch is why there are two bulges, and it answers the classic puzzle: if the Moon pulls the water toward it, why is there also a high tide on the opposite side? Because on the far side the Moon pulls the water less than it pulls the solid Earth out from under it — so the water is effectively left behind, bulging outward. As Earth rotates, each location sweeps through both bulges, giving roughly two high tides and two low tides per day.
The strength falls off steeply, as (one power steeper than gravity's , because it's a difference across the planet). The Moon wins over the far larger but far more distant Sun by about 2 to 1. When Sun and Moon align — at new and full Moon — their bulges add into extra-large spring tides; when they sit at right angles (first and last quarter), the bulges partly cancel into gentle neap tides. The same stretching, taken to an extreme near a black hole, is what would "spaghettify" an infalling object.