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Lee,I don't understand how gravitational forces vectored from the sun and moon do not count?
Dave Lammel asked the Naked Scientists: Since gravity would be pulling outward in all directions on the core, would not the very centre be filled with lighter material?
Quote from: Dave Lammel on 07/12/2009 10:30:02Dave Lammel asked the Naked Scientists: Since gravity would be pulling outward in all directions on the core, would not the very centre be filled with lighter material? No! At the exact centre there is zero gravity, definitely not being pulled in all directions. Mathematically, this is how you calculate the net local gravity but the result is the actual net local gravity i.e. zero. Apart from at the exact centre there is always some gravity. And this gravity is always pulling towards the centre. For any position inside the Earth, regardless of the absolute strength of local gravity, heavy (denser) material will still be under a greater force than lighter material in the same region. So heavier stuff will always tend toward the centre more than light stuff.Also, regardless of local gravity, the actual pressure of all the stuff above you will ensure that anything near the middle is fairly dens. The very centre will be at zero gravity but under enormous pressure. If there were gas at the centre (I doubt it but I'm not a geophysicist) it would be gas that is as dens as molten iron and only remains gas due to the very high temperature, caused by the pressure.