Tidal force

Gravitational effect also known as the differential force and the perturbing force

The tidal force or tide-generating force is the difference in gravitational attraction between different points in a gravitational field. It causes different parts of bodies to be pulled unevenly, so that those bodies are being stretched towards the attraction. Tidal force is the differential effect of gravity across an extended body.

From Wikipedia, under CC BY-SA. More on occurri.