is there gravity at the centre of the earth?, page-29

To add to the debate, gravity is not constant, it is dependant on mass. This is why geophysicists have to due topographic corrections when doing gravity surveys, because different amounts of land mass will influence the data.

So gravity will increase the closer you are to the mass or body, or in this case the earth. Gravity has less and less pull the further away from the mass you are. This is how we can keep things like satellites in orbit, they are far enough away to be outside of the influence of gravity trying to pull them to the earth, but just close enough to keep them from flying into space.

Wiki gravity on Jupiter, as this is a much larger mass than Earth it will have a higher gravitational pull.

http://www.universetoday.com/15110/gravity-of-jupiter/