Comparing Gravitational & Electrostatic Forces (AQA A Level Physics)

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

Similarities between gravitational and electrostatic fields

• The field lines around a point mass and negative point charge are identical
• The field lines in uniform gravitational and electric fields are identical
• Both forces follow inverse square law relationships with distance
• Both gravitational field strength and electric field strength follow an inverse square law (1/r²) relationship with distance in a radial field
• Both gravitational potential and electric potential both follow an inverse (1/r) relationship with distance
• The equipotential surfaces are spherical around a point mass or charge and equally spaced parallel lines in uniform fields
• The work done by either field is equal to the product of the mass or charge and change in potential

Differences between gravitational and electrostatic fields

• 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
• Gravitational fields are relatively weak compared to electric fields as the gravitational constant G is much smaller than the Coulomb constant k