Hear me out, gravity pulls us towards itself. It is determined by the magnitude of mass of that object. As we go deeper in earth, the amount of mass ‘under’ us decreases and so doesn’t the gravity also decrease? Have been thinking about it since I was 12, I am 15 now 🙂
Edit : It wouldn’t be right to thank just one of you by replying as I have seen some other people do but thanks for all the replies, I really appreciate it.
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If the Earth was a ball of uniform stone, then you’re right, gravity would get weaker as you went down, since more of the stone would be pulling you up.
The Earth is not a uniform ball of stone though. The surface is made from relatively light, fluffy stone (it’s floating on top of everything else after all), and the centre holds a lot more of the mass, being a giant chunk of molten metal.
So as you go down from the surface, the rock above you really doesn’t contribute much to the total mass of the Earth. Most of the Earth will still be under you for quite a while, but you’re getting closer to it, which increases gravity. (Gravity gets stronger with mass, weaker with distance)
Eventually, you will reach a point where the gravity starts to get weaker again because you’re starting to pass the actual heavy substance, and from there it decreases to 0 at the centre of the Earth, as you’d expect.
It does not increase when you go deeper, in fact it decreases.
Think about it like this. Here on the surface of the planet, there is some gravity. And if you are in the very centre of the Earth, there the mass is distributed evenly around you (let’s assume Earth is perfect that way). This means that the mass above your head is evened out by the mass under your feet, and the mass to the left by the mass to your right etc. This means that the net force is zero.
You’re going from some gravity to no gravity, so it must decrease. It may not decrease all the way (perhaps it remains constant for a while; or maybe it increases a bit), but in the end it must decrease.
Now, the neat part is that it decreases linearly. Sadly, I can’t remember the math involved to show it. The important part is that you’ll also have a bunch of mass above you, pulling you up, and that counteracts a part of the pull downwards from the rest of the planet.
You are right, gravity does increase (i.e. the force of gravity on a particular amount of mass does increase) as you get deeper in the Earth, up to a certain point. After that it decreases to zero at the center.
The reason for this is that the outer portion of the Earth is less dense, has less mass per unit volume, than the interior of the Earth.
As you know, the force of gravity between two objects depends on the mass of the objects and the square of the distance between them. It is increased by larger mass and decreased by larger separation.
Because of the fact that the crust is significantly less dense than the stuff below it, and the stuff immediately below the crust is also less dense than the core, as it happens, the effect of getting closer to the mass beneath you is larger than the effect of losing the contribution of the portion of the crust that’s now above you (for the first couple thousand kilometers of your imaginary borehole).
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The gravity should decrease the deeper you go as the earths mass will be more spread around you instead of all of it being below you.
However the closer you are to the earth core the less centrifugal force will be applied to your body, thus making you heavier.
This is why you weigh more on the ice poles but also the fact that the earth is oval so the poles are naturally closer to the core than the equator is
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As you travel towards the center of the earth gracity actually increases until it reaches its maximum at the core mantle boundary then it decreases as you travel from there to the core
https://i.stack.imgur.com/Zz4VN.png
Edit. Most of the comments are incorrect in reality. Aside from this comment, there are two others that are correct. Increases then decreases
If the earth were a constant density, gravity would decrease as you went nearer to the centre. But the core of earth is much denser, so as you pass through the lighter, outer layers, you get closer to that dense core and gravity increases (slightly). Once you reach the denser material, gravity gradually decreases as you get closer to the centre.
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