7.4.7 Comparing Gravitational & Electrostatic Forces

• The similarities and differences between gravitational and electrostatic forces are listed in the table below:

Table Comparing G and E Fields 

• The key similarities are:
  • The magnitude of the gravitational and electrostatic force between two point masses or charges are inverse square law relationships
  • The field lines around a point mass and negative point charge are identical
  • The field lines in a uniform gravitational and electric field are identical
  • The gravitational field strength and electric field strength both have a 1 / r² relationship in a radial field
  • The gravitational potential and electric potential both have a 1 / r relationship
  • Equipotential surfaces for both gravitational and electric fields are spherical around a point mass or charge and equally spaced parallel lines in uniform fields
  • The work done in each field is either the product of the mass and change in potential or charge and change in potential

• The key differences are:
  • The gravitational force acts on particles with mass whilst the electrostatic force acts on particles with charge
  • The gravitational force is always attractive whilst the electrostatic force can be attractive or repulsive
  • The gravitational potential is always negative whilst the electric potential can be either negative or positive