Sure you remember when I have said that the earth is round. Then, over time, they tell you is not round, but potato-shaped due to the rotation of the same. And they stay there.
Fortunately, since you are the old enough to tell you that not only shaped potato, but also, gravity, this constant to tell you in school that are 9.8 m / s is not as constant as will the Do you sell.
The gravity on Earth varies from place to place as you can see in the picture taken Champ and Grace, two satellites that have been responsible for it. Data were analyzed by the University of Potsdam in Germany and therefore the form is called “Potsdam Potato” (that curious).
Vary for several reasons, and may be the height of things (in a mountain is different than at sea level) and other varies by mere soil composition. Because, as you might remember, the gravitational force (no waves) are based in the field and distance, mass and distance (as Newton said). And there are areas where the mass, density, different from others making has different severity.
Come pesáis not the same as where you are on Earth, but do not rejoice because although you do not weigh them as well, the dough if you have it.