Editing Tidal force (section)

== Explanation ==
[[File:Tidal field and gravity field.svg |thumb |upright=1.3 |Figure 2: Shown in red, the Moon's gravity ''residual'' field at the surface of the Earth is known (along with another and weaker differential effect due to the Sun) as the ''tide generating force''. This is the primary mechanism driving tidal action, explaining two simultaneous tidal bulges.

Earth's rotation accounts further for the occurrence of two high tides per day on the same location. In this figure, the Earth is the central black circle while the Moon is far off to the right. It shows both the tidal field (thick red arrows) and the gravity field (thin blue arrows) exerted on Earth's surface and center (label O) by the Moon (label S).  The ''outward'' direction of the arrows on the right and left of the Earth indicates that where the Moon is at [[zenith]] or at [[nadir]].]]

When a body (body 1) is acted on by the gravity of another body (body 2), the field can vary significantly on body 1 between the side of the body facing body 2 and the side facing away from body 2. Figure 2 shows the differential force of gravity on a spherical body (body 1) exerted by another body (body 2).

These ''tidal forces'' cause strains on both bodies and may distort them or even, in extreme cases, break one or the other apart.<ref name=Penrose>
{{cite book
 | title=The Emperor's New Mind: Concerning Computers, Minds, and the Laws of Physics
 | author=R Penrose
 | page=[https://archive.org/details/emperorsnewmindc1999penr/page/264 264]
 | url=https://archive.org/details/emperorsnewmindc1999penr
 | url-access=registration
 | quote=tidal force.
 | isbn=978-0-19-286198-6
 | date=1999
 | publisher=[[Oxford University Press]]
}}</ref> The [[Roche limit]] is the distance from a planet at which tidal effects would cause an object to disintegrate because the differential force of gravity from the planet overcomes the attraction of the parts of the object for one another.<ref name=Blanc>
{{cite book
 | title=The Solar System
 | page=16
 | url=https://books.google.com/books?id=Je61Y7UbqWgC&q=tidal+force&pg=PA16
 | author=Thérèse Encrenaz|author-link=Thérèse Encrenaz
 | author2=J -P Bibring
 | author3=M Blanc
 | isbn=978-3-540-00241-3
 | date=2003
 | publisher=Springer
}}</ref> These strains would not occur if the gravitational field were uniform, because a uniform [[field (physics)|field]] only causes the entire body to accelerate together in the same direction and at the same rate.