Tide Producing Force

The tide-producing force is the small residual of the Moon’s and Sun’s gravity after subtracting the average pull that holds Earth in orbit: it is the difference in gravitational attraction across Earth’s diameter, falling off as the inverse cube of distance. That is why the nearer Moon dominates the Sun despite the Sun’s far greater mass. The force raises bulges on the near and far sides, giving two tides per day, modulated by lunar phase and distance.