What is the cause of the rotation of the planets

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Discussion Overview

The discussion centers on the causes of the rotation of planets and the Sun, exploring concepts related to angular momentum, gravitational interactions, and tidal forces. It encompasses theoretical explanations and observational phenomena.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • Some participants propose that the conservation of angular momentum is a key factor in the rotation of planets and the Sun.
  • One participant suggests that particles falling into a gravity well travel in a spiral path, which allows them to preserve momentum and imparts spin to the accreting body.
  • Another participant discusses the idea that rotating objects will continue to rotate until acted upon by an external force, noting that tidal forces can synchronize rotation with revolution, as seen with the Earth and its moon.
  • It is mentioned that tidal forces do not stop rotation but can influence the rotational dynamics of smaller bodies in the solar system.
  • Examples are provided, such as the Earth-Moon system and Mercury's rotation relative to its revolution around the Sun.

Areas of Agreement / Disagreement

Participants express various viewpoints regarding the causes of planetary rotation, with no consensus reached on a singular explanation. Multiple competing ideas remain present in the discussion.

Contextual Notes

The discussion does not resolve the complexities of how different forces interact to influence rotation, and assumptions regarding the effects of tidal forces and angular momentum conservation are not fully explored.

Bjarne
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What is the cause of the planets (and the Suns) rotation
 
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vincentm is correct. Particles falling into a gravity well travel in a spiral path. It is not unlike flushing a toilet. Traveling in a spiral path allows them to preserve momentum until absorbed. This imparts spin to the accreting body [star, planet, etc.].
 
Furthermore, the natural state of affairs is that rotating objects will continue to rotate until something comes along to stop it. For the larger bodies in the solar system, there aren't any significant effects on their rotation. But for the smaller bodies...

The main effect on rotation is tidal forces, which don't work to stop rotation, but to synchronize it with revolution. The Earth is big enough and near enough (and has had enough time) to coerce the moon into making one rotation once per revolution. Similarly, the Sun has locked Mercury into making 3 rotations per 2 revolutions. You also see this with many (most?) of the moons in the solar system.
 

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