New to Physics. Can you explain?

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Discussion Overview

The discussion revolves around the concepts of rotational motion, tidal locking, and the forces that influence the spinning of celestial bodies, particularly focusing on the Earth, Moon, and Sun. Participants explore the reasons behind the Earth's rotation and its relationship with the Moon and the Sun, as well as the implications of tidal locking.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants assert that the Earth continues to spin due to the absence of external forces acting upon it, while others challenge this notion by discussing the role of the Sun as an external force.
  • There is a belief expressed that only stars can induce spinning in celestial bodies, leading to questions about why the Sun does not keep the Earth in a locked position like the Earth does with the Moon.
  • Some participants mention that the Moon is not fully locked in position, as its rotation allows for a phenomenon called libration, which enables observers on Earth to see more than 50% of its surface over time.
  • A hypothesis is presented regarding the relationship between distance and tidal locking, suggesting that bodies closer together, like the Earth and Moon, may achieve tidal locking more rapidly than those further apart.
  • One participant emphasizes that the Earth does not have the capability to spin a body of mass in the same way the Sun does, implying a difference in gravitational influence.
  • Another participant clarifies that the Moon became tidally locked to the Earth due to gravitational interactions, rather than the Earth causing the Moon to spin.

Areas of Agreement / Disagreement

Participants express differing views on the mechanisms of rotation and tidal locking, with no consensus reached on the reasons behind the Earth's spinning or its relationship with the Moon and Sun.

Contextual Notes

Some claims rely on assumptions about gravitational forces and the nature of tidal locking, which are not fully explored or resolved in the discussion. The implications of orbital mechanics and the specific conditions required for tidal locking are also not definitively established.

consistency
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I. Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

They say the Earth keeps spinning because it started spinning and now there is no external force applied to it to stop it.

The Sun is an external force.

I actually believe that only Stars can make bodies of mass spin. Hence the Earth and other planets like Jupiter have their satellites in a locked position(not spinning).

Why doesn't the Sun keep the Earth in a locked position like the Earth keeps the Moon in a locked position? or like Jupiter keeps its satellites in a locked position?
 
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I am pretty sure that eventually the Earth will stop rotating, but it will take quite a long time. The Earth is quite massive.
 
The moon isn't quite in a locked position, it rate of rotation coincides with it's rate of orbit, so that the same hemisphere faces the earth, but due to the axis of rotation versus plane of it's orbit, and the elliptical orbit of the moon, (and the position of an Earth observer) over time an Earth bound observer can see 59% of the moons surface due to libration:

http://en.wikipedia.org/wiki/Libration

That wiki article contains a link to tidal locking:

http://en.wikipedia.org/wiki/Tidal_locking
 
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This is actually a guess on my part, but I think it's because the torque that causes the effect falls off like 1/r which means something with a smaller separation distance (such as the Earth/Moon distance) will fall into tidal locking faster than something with a large separation distance. That's a guess though, I haven't put pen to paper on that one.
 
khemist said:
I am pretty sure that eventually the Earth will stop rotating, but it will take quite a long time. The Earth is quite massive.

Re-read my question.

rcgldr said:
The moon isn't quite in a locked position, it's orientation relative to it's orbit oscillates somewhat, allowing an Earth bound observer to see about 59% of the moon's surface over time.

The Moon doesn't spin 100% like the Earth does around the Sun. It oscillates because its fighting to get out of Earth's orbit. 59% isn't much. 59% - 50% = 9% of oscillation.

The Earth doesn't seem to have the "Power" to spin a body of mass like the Sun does.
 
consistency said:
I. Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

They say the Earth keeps spinning because it started spinning and now there is no external force applied to it to stop it.

The Sun is an external force.

I actually believe that only Stars can make bodies of mass spin. Hence the Earth and other planets like Jupiter have their satellites in a locked position(not spinning).

Why doesn't the Sun keep the Earth in a locked position like the Earth keeps the Moon in a locked position? or like Jupiter keeps its satellites in a locked position?

This is incorrect. Any spinning object keeps spinning unless a force is applied, like the law states. The Earth and all the planets and moons and everything else are spinning because they were spinning when the gas cloud that formed the solar system first collapsed and formed them. Had there not been enough mass within this cloud to give the Sun enough mass to ignite fusion, and hence it would not have been a star, it would still have been spinning and so would anything else that had formed with it.

The moon is tidally locked to the Earth because of Tidal Locking: http://en.wikipedia.org/wiki/Tidal_locking

The Earth isn't tidally locked to the sun because the gravitational gradiant isn't sufficient enough to cause that effect. If you look at Mercury however, it IS tidally locked in a 3:2 orbital resonance. The eccentricity of its orbit causes this to be stable. The moon is in a 1:1 orbital resonance with the Earth because of its nearly circular orbit with low eccentricity. (And even then it isn't perfectly synced, there is a small shifting back and forth that allows us to view a little bit more than 50% of the moon over the course of its orbit.)

The Earth doesn't seem to have the "Power" to spin a body of mass like the Sun does.

The Earth caused the moon to STOP rotating as fast as it was and become locked. It did not cause the moon to spin.
 

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