Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Assad Ali on 14/12/2010 10:30:03

Title: Does gravity change in the centre of the Earth?
Post by: Assad Ali on 14/12/2010 10:30:03

Assad Ali asked the Naked Scientists:
   
Would the force of gravity change if you were to tunnel down into the Earth?

What do you think?

Title: Does gravity change in the centre of the Earth?
Post by: Chemistry4me on 14/12/2010 10:59:48

Yes, the force of gravity on you increases.

Title: Does gravity change in the centre of the Earth?
Post by: CliffordK on 14/12/2010 11:04:15

Yes.

Obviously in the middle of the earth, one would have all the mass above a person and one would essentially be weightless (0 gravity).

According to the notes I found on the web, the earth is not a uniform density, and thus it was predicted that the highest gravity was predicted to be found at the Core/Mantle Boundary, of about 10.7 m/s², at a depth of about 2885 km (note, it is about 9.8 m/s² at the surface).  As you descend further, the gravity would decrease to 0 in the middle.

http://www.chsfootball.net/earth_g_2.doc

Title: Does gravity change in the centre of the Earth?
Post by: Chemistry4me on 14/12/2010 11:07:20

Quote from: CliffordK on 14/12/2010 11:04:15

  As you descend further, the gravity would decrease to 0 in the middle.

Why zero and not infinity?

Title: Does gravity change in the centre of the Earth?
Post by: imatfaal on 14/12/2010 12:33:19

We seem to get this question about once a week at present.  Clifford's answer that it diminishes in general is correct; I hadnt realised that specifically that due to non-uniformity actually goes up for a while.

C4Me - the reason it drops is, that presuming symmetry, one only feels attraction from the sphere 'inside' your position, everything outside your position cancels out.  Both Newton and Gauss proved this - the easist wiki/google search is on "Newtons Shell Theorem"

Title: Does gravity change in the centre of the Earth?
Post by: Chemistry4me on 14/12/2010 12:46:05

Quote from: imatfaal on 14/12/2010 12:33:19

C4Me - the reason it drops is, that presuming symmetry, one only feels attraction from the sphere 'inside' your position, everything outside your position cancels out.  Both Newton and Gauss proved this - the easist wiki/google search is on "Newtons Shell Theorem"

Oh yes, thanks for clearing that one imatfaal. I knew it was past my bed time [:)]