The intensity of gravity g is easy to measure with a pendulum and it is not equal in all places.

   Gravity at the centre of the planet is nil and it increases linearly until it reaches the surface.

   The value of g, away from the surface of the planet decreases with distance. 

    Although we are not going to demonstrate this, you should know that the value of g is determined by the law:

  Where G is the universal gravitational constant, M is the mass of the planet and r the distance to the centre. 

   If you want to see how g varies again click here.