What is the single best electrical ground on planet earth?

Where does gravity have the least overall affect on something on earth?

• Too all scientists and/or just cool minded people. Bit of a confusing question at first but let me explain. I've seen many other answers to similar questions such as "Where do you weigh the least on earth?", "Where on the planet does gravity have the least affect on you". Almost all of the answers state on the tallest mountain, the furthest away from the 'centre' of the earth, or the equator (because it's the furthest away from the centre). I have a theory and I'd like peoples comments or some serious scientific reasoning, I'm not a scientist, I've not been to university, I'm just open minded. Please correct me if I'm wrong with anything. Gravity is a force that can be split into horizontal and vertical forces which are equal to the same force in one direction. Gravity also doesn't come from the centre of the earth, it comes from each and individual particle on the planet, all acting on us from all places on the planet, the fact that they're in equilibrium to each other combined with the reaction normal + friction means that we are stable and do not move unless external forces are acting on us. Getting back to people's answers such as "The equator", people state this answer I'm guessing because the earth is 'Oval' shaped and the equator is the peak, thus being furthest away from the centre, however if you was stood on the equator there is more ground/mass vertically beneath you, than if you where stood on the north pole/south pole. If there is more mass vertical to you, surely gravity is greater than if that mass was spread out horizontally. Is it not? So thats my first question/theory. Secondly if you where placed on the earths centre of gravity the overall affect of gravity would be 0? People say that gravity has less effect on you're on the top of a mountain 8km from sea level, even though you are further away from the majority of the earths gravitational pull, you are still receiving all gravitational forces that are below you. Would gravity have a less overall affect if you where 8km below sea level, or at what point do you think gravity has less affect below rather than above sea level? If I was standing 8km below sea level surely the 8km tall amount of land above me would have a gravitational pull thats opposite to the overall gravitational pull of the earth below me. As they are opposite the overall affect of gravity would be lower than if all of gravity was pulling in one direction. The deepest anyone has apparently been into the earth is 3.9km (TauTona gold mine), I wonder if the gravitational pull of the earth above that point reduced the overall gravitational pull compared to say the peak of Mount Everest. Hmmm...What do you think?

• Answer:

  In answer to your questions / theories directly... Number 1: You are correct, at the equator the force for gravity DUE TO MASS is greater than at the poles due to the oblate spheroid shape of the planet, the equatorial bulge. This is for the reason you have given, i.e. the mass (M) between you and the centre of the Earth (g) is greater. However... another major thing to consider is that the closer you are to the centre of mass the greater the force. Therefore due to the equatorial bulge at the equator you are farther from the centre of the Earth and therefore the gravitational pull is less. Finally... centripetal force also lessens the pull of gravity as the earth is spinnin most at the equator and less ta the poles. Therefore the overall net effect of these 3 things is a lower gravitational acceleration at the equator than at the poles. At the equator it is 9.780 ms^-2 whilst at the poles it is roughly 9.832 ms^-2 at the poles. Number 2: Yes, you are correct that when in the centre the mass betwee you and the centre of mass would be zero therefore the mass acting on you would be the mass above you which would actualy pull you out from the centre not in. Therefore you are also correct were you to go down into a cave 8km below the surface the land above you would also exert an attractive force, as the Earth is 6370 km thick youwould still have 6362 km of mass pulling you downward so the reduction due to the mass above and loss of mass below would be so negligible you would be lucky to measure it! Also the majority of the Earths mass is held in the core and mantle, 8km wouldn't get you past the crust in most places which is relatively light so even less of the mass would be taken care of by dropping this small depth. Were you to be half way down into the centre of the earth the difference would be much greater.. It can be worked out mathematically but I'm not doing that now! Gravity at the peak of Everest is less than at sea-level and at the top your weight would be reduced by around 0.2%, even in geosynchronous orbit the force of gravity is around 90% of normal so Everest is a very teeny tiny blip on the face of things! In fact, the mariana trench is deeper than Everest is high however the weight of the water would make it very uncomfortable down there!