Tidal force, also called tide-generating force, is the differential gravitational effect across an extended body caused by the spatial variation in the gravitational field of another body. It arises because gravity follows an inverse-square law, so the attractive force is stronger on the near side of the body and weaker on the far side compared to its center. This difference stretches the body along the line connecting its center to the source of the gravitational field, producing two tidal bulges, one toward the attracting body and one away from it. The concept is explained by the law of universal gravitation. The gravitational force between two point masses is proportional to their masses and inversely proportional to the square of the distance between them. Tidal forces are a residual effect of gravity and occur universally wherever gravitational fields have gradients across finite-sized objects.
