The famous expression for the field intensity of gravity is only valid if we are calculating the field intensity outside the planet. Inside the planet, it is possible to prove, using Gauss' theorem, that the field intensity depends only on the mass that is nearer to the centre of the planet than the point at which we are measuring the field.

Click on to study the field intensity of gravity inside and outside a planet.

Furthermore, on the surface of a rotating planet, it is necessary to take into account the apparent change in the force of gravity due to the centrifugal force caused by rotation.

Click on to observe these effects.