Strength of Gravity approaching centre of Earth (1 Viewer)

[Amundies]

In the Half-yearly Physics exam we had, the 2nd question in the multiple choice was something along the lines of: "What happens to the strength of gravity as you approach the centre of the Earth?" The question involved scientists digging a long tunnel to the centre of the Earth and stuff, but all that was irrelevant.
The two possible answers were:
1). Increased as you go to the centre.
2). Decreased to 0 as you approached the centre.
The answers to the test said it was the first answer, and so did most of the students who sat the test. However, the teachers decided that it was probably the second answer as one student had said that it was that (and given his reasoning). Keeping in mind that we're not supposed to go beyond the Physics syllabus, what would the answer to the question be and if you could provide reasons that'd be great too.

 

[soloooooo]

It would be basically 0 as the force components from all directions cancel out.

 

[SpiralFlex]

Do you have Fullerton?

 

[D94]

According to PREM, the strength of gravity goes to zero: http://geophysics.ou.edu/solid_earth/prem.html

What happens beneath the Earth's surface is different to what happens above (i.e. with altitude, strength of gravity also decreases).

 

[Amundies]

Do you have Fullerton?

Yes I do, and he said that he'd be willing to give both of those answers as correct.

According to PREM, the strength of gravity goes to zero: http://geophysics.ou.edu/solid_earth/prem.html

What happens beneath the Earth's surface is different to what happens above (i.e. with altitude, strength of gravity also decreases).

That's true, but what it also says that the strength of gravity increases then decreases twice before going down to 0 right at the centre of the Earth. It does not go down straight to 0 m/s^2 linearly.

 

[premskies]

I had the same question in my exam (and it was also the 2nd MC question). Answer is definitely decreases to 0 as you approach centre.

 

[D94]

That's true, but what it also says that the strength of gravity increases then decreases twice before going down to 0 right at the centre of the Earth. It does not go down straight to 0 m/s^2 linearly.

That's irrelevant information, it approaches 0 as you go towards the centre, not as it approaches the outer core or whatever. However, it should be noted that since the density of the layers differ, the strength of gravity differs. You cannot definitively say it increases only.