The gravitational center of the Earth

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Discussion Overview

The discussion revolves around the concept of the gravitational center of the Earth, particularly in relation to the gravitational effects of the Moon and the Earth-Moon system. Participants explore the implications of gravitational forces at the Earth's center and the barycenter of the Earth-Moon system.

Discussion Character

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

Main Points Raised

  • One participant suggests that the area of zero gravity near the Earth's center may have shifted due to the Moon's gravitational field, proposing that this area orbits around the Earth's center.
  • Another participant clarifies that gravitational forces are not "felt" in free fall, and the perception of zero gravitational force depends on the frame of reference.
  • A participant notes that the Earth-Moon system orbits around a center of mass, or barycenter, which is located about 1,700 km below the Earth's surface.
  • It is emphasized that an object at the barycenter would still experience gravitational attraction towards the Earth's center, indicating that the location of gravitational force cancellation remains unchanged despite the orbiting of the Earth and Moon around their mutual center of mass.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the Moon's gravitational influence on the Earth's gravitational center, and the discussion remains unresolved regarding the effects of the Earth-Moon system on gravitational forces experienced at the Earth's center.

Contextual Notes

The discussion includes assumptions about gravitational forces and frames of reference that are not fully explored, particularly regarding the implications of the barycenter's location and its effects on gravitational perception.

qnt200
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We know that gravitational forces are nullified near the center of the Earth, so the gravitational field's influence is not felt. Is it because of the Moon's gravitational field that the area of zero gravity has shifted away from the center of the Earth? If this is the case, this eccentric area will orbit around the center of the Earth due to the moon's orbit.
 
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The gravitational field is never ”felt” in free fall regardless of where you are. Whether the gravitational forces equate to zero depends on your frame of reference.

If you want to consider the Earth-Moon system, them the center of mass is indeed not at the center of the Earth.
 
The Earth and Moon orbit about the center of mass of the Earth-Moon system. This point, called the barycenter, is about 1,700 km below the Earth's surface.
 
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However, it's important to stress that an object placed at the barycentre would still be attracted towards the centre of the Earth. I.e. the fact that the Earth and the Moon orbit their mutual centre of mass doesn't affect where the forces produced by the Earth on itself cancel out. This follows from the point Orodruin made - everything on/inside the Earth is in free fall w/r to the Moon, but not w/r to the Earth itself.
 

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