Point Mass Approximation (Cambridge (CIE) A Level Physics) : Revision Note

Point mass approximation

• For a point outside a uniform sphere, the mass of the sphere can be considered to be concentrated at a single point at its centre of mass

  • A uniform sphere is one where its mass is distributed evenly

• The gravitational field lines around a uniform sphere are therefore identical to those around a point mass

• An object can be regarded as a point mass when:

It has an even mass distribution and the distance being considered is larger than its size

• This applies to field lines around planets

Gravitational field lines around a planet

Gravitational field lines around a uniform sphere are identical to those on a point mass