The gravitational center of the Earth

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SUMMARY

The gravitational center of the Earth is influenced by the Earth-Moon system, where the barycenter is located approximately 1,700 km below the Earth's surface. Gravitational forces are nullified near this center, meaning the gravitational field is not felt in free fall. The Moon's gravitational field does not shift the area of zero gravity; rather, it is the frame of reference that determines the perception of gravitational forces. Objects at the barycenter remain attracted to the Earth's center, despite the Earth and Moon orbiting their mutual center of mass.

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  • Understanding of gravitational forces and fields
  • Knowledge of the Earth-Moon system dynamics
  • Familiarity with the concept of barycenter
  • Basic principles of free fall and frame of reference
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  • Research the concept of barycenter in celestial mechanics
  • Explore gravitational field variations within planetary bodies
  • Study the effects of the Moon's gravity on Earth’s tides
  • Investigate the principles of free fall in different gravitational contexts
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Astronomers, physicists, students of planetary science, and anyone interested in the dynamics of gravitational forces within the Earth-Moon system.

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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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