2023-08-29 11:00:00
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Did you know that you do not weigh the same at all points on the planet? Depending on the area you are in, the scale can reach vary by almost 0.7 kg. That is, if you weigh 100 kg in one place, maybe in a different one, the scale will show 99.3 kg. And no, it’s not a matter of you losing weight or that the scale is broken. The explanation lies in the force of gravity.
our planet is much more complex than it seems and, if everything were an ideal situation in which there was no rotation, all the layers were the same or the density of the materials were the same, the entire earth’s surface would be uniform and your scale would read the same everywhere . But it is not that simple.
ESA
First global map of the gravitational field obtained by the GOCE Mission. The areas in red are regions of the surface with greater gravity, while in the blue it is less.
In fact, the force of gravity does not even behave in a uniform way when we move towards the center of the planet and it acquires values unexpectedly high the closer we get to the metallic nucleus. What does this mean exactly? Well, although it would be logical for it to descend, at a depth of 3,000 km the value of gravity is considerably higher on the surface. Does this mean that there is no center of gravity? What then is its value in the Earth’s core?
THE IDEALITY
In an ideal situation in which the inner layers of the Earth were perfectly uniform, going down through a tunnel facing the center of the planet, gravity would go down. Thus, on the surface itself, it would reach its greatest value, since the force would attract you towards the great mass that is the planet, located below you.
As you descended, there would begin to be mass above your head, which would also generate a certain force of gravity towards it, and therefore upwards. In fact, the deeper you go, the greater that contribution would be, since the amount of earth above your head would be greater and greater. But upon reaching the center, since you would be surrounded by the same amount of mass in all directions, all the forces around you would cancel each other out, placing you at a point where the sensation of gravity would be nil.
Why are the planets round?
THE INTERNAL STRUCTURE
But as you can imagine, the reality is a very different situation. And it is that not all the interior of the planet is the same, so, to understand this issue it is necessary to know what the structure of planet Earth is, starting with the simplest: the visible part. The entire rocky surface is covered by a layer, called atmosphere, whose thickness reaches 1,100 km, composed of essential gases for the development of life. Covering the surface is the hydrosphereextended to almost 4 km deep and made up of all the water on the planet.
The Earth crust It is the area where life develops. It reaches up to 100 km deep and is made up mostly of rocks and various accumulated chemical elements, such as oxygen, silicon, iron, calcium or sodium. Just below her, stretches the manto up to 2,900 km, a solid zone composed mainly of magnesium and silicon oxides.
Shutterstock
Diagram of the structure of the Earth. From the outer to the inner part, we have the earth’s crust (crust), the mantle (mantle), the outer core (outer core) and the inner core (inner core).
Finally, the interior of the planet is the core. It is divided into an outer part of 2,200 km which is thought to be rigid, but has troughs and peaks on its surface. For its part, the inner core is completely metallic and stands out for having temperatures that can reach up to 6,650 ºC and an average density of 13. This means that the pressure inside, measured in GigaPascals, is millions of times the that exists on the surface.
Discovered a second metallic core even deeper inside the Earth
A VERY DIFFERENT REALITY
Therefore, far from the proposed ideality, reality presents a very different scenario: the Earth it is not uniform and the metallic core is much denser than the mantle and crust. Therefore, the moment you start to face deeper into the Earth, everything changes: the densest material will generate much more gravity than the less dense material.
So if you start digging, as you move away from the surface and get closer to the metallic core of the planet, the force of gravity will increase more and more, because the material above your head will not be dense enough to counteract the attraction generated by that central area. This “pull” is so great that at about 3,000 km, just at the entrance of the nucleus, the force of gravity reaches its greatest value: 10, 7 m/s2. It must be taken into account that on the surface its value is 9.8 m/s2.
Dziewonski, A. M. (1981)
Variation of gravity on Earth as a function of depth.
From there, the forces within the nucleus itself will compensate in an equivalent way, allowing you to find the zero gravity point toward the center of the nucleus. Although it is true that this nucleus is not completely uniform and it is estimated that the point of zero gravity would not have to be right in the center, it would exist at some very close point that cancellation of forces that would allow you to experience the sensation of weightlessness.
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