Comparing Gravitational & Electrostatic Forces (AQA A Level Physics): Revision Note

Gravitational v electrostatic forces

• 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 ($\frac{1}{r^2}$) relationship with distance in a radial field

• Both gravitational potential and electric potential follow an inverse ($\frac{1}{r}$) 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