Tidal Force

AE Phe binary
Image from Steve Bowers
Tidal forces pull the stars in this contact binary pair into shapes that fill their respective Roche Lobe

A secondary effect of the force of gravity, arising from the fact that gravitational effects are not constant across the width of an object: the portions nearer the source of gravity are subject to a stronger pull, and the portions further away are subject to a weaker pull. Thus the near side is relatively accelerated towards the source and the far side has a relative acceleration in the opposite direction. The steeper the gradient, the stronger the effect. Low level tidal forces may cause bodies of water or other liquids on an object to have tides. Tidal forces may also cause a body to flex somewhat, and if they are strong enough may be a cause for geothermal activity in some planets or moons. These forces may eventually cause a rotating object to slow so that its period of revolution and its period of rotation around the nearby sun or planet are equal. At the extreme, if a body is sufficiently deep within a gravitational well it may be pulled apart by tidal forces (see Roche limit).

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    The distance from a large body or primary within which tidal forces would disrupt or disintegrate a satellite.
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Development Notes
Text by Stephen Inniss
Initially published on 27 February 2014.