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 may be considered to be a point mass at its centre

  • 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:

  Its mass is so small its location is defined at a single point

• This applies for 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