Test yourself

Force Fields

Fields are a convenient mathematical idea for representing how forces and potential energies change in a region of space around an object. Forces arise from the interactions between objects.

Illustrative background for Gravitational forceIllustrative background for Gravitational force ?? "content

Gravitational force

  • Gravitational force arises because of the interaction between two masses.
  • We map gravitational fields by considering the effect of that field on a point mass.
Illustrative background for Electrostatic forceIllustrative background for Electrostatic force ?? "content

Electrostatic force

  • Electrostatic force arises because of the interaction between two charges.
  • We map electric fields by considering the effect of that field on a point positive charge.
Illustrative background for Magnetic forceIllustrative background for Magnetic force ?? "content

Magnetic force

  • Magnetic force arises, fundamentally, because of the interaction between charges that have relative motion between them.
  • When we map magnetic fields, we simplify matters by considering the effect on a small bar magnet, or magnetic dipole.

Comparing Gravitational and Electrostatic Forces

Gravitational and electrostatic forces have similarities and differences.

Illustrative background for Similar ideasIllustrative background for Similar ideas ?? "content

Similar ideas

  • If we consider both as fields, we can apply similar ideas.
    • We use field lines to represent the direction of the force on a point particle.
    • We use the concept of equipotential lines and surfaces.
Illustrative background for SimilaritiesIllustrative background for Similarities ?? "content


  • When considering point objects, both forces have inverse-square laws.
  • The field line patterns around point objects are radial - like spokes on a bicycle wheel.
    • The field lines get further apart as the distance increases from the point object. This indicates that the force on a test particle gets smaller.

Similarities 2

  • Equipotential lines/surfaces around point objects are concentric circles or spheres.
    • Those equipotential lines get further apart for equal changes in potential between lines.
  • You can add field strengths from two or more particles vectorially. This means you can determine field line patterns from complex arrangements of particles.
Illustrative background for DifferencesIllustrative background for Differences ?? "content


  • The force between masses is always attractive.
    • Field lines always point towards masses.
    • Potential-distance graphs for gravitation are always negative.
  • The force between charges can be either attractive or repulsive.
    • Field lines always point away from positive charges and towards negative charges.
    • Potential-distance graphs for a point charge can either be positive or negative.

Jump to other topics

1Measurements & Errors

2Particles & Radiation


4Mechanics & Materials


6Further Mechanics & Thermal Physics (A2 only)

7Fields & Their Consequences (A2 only)

8Nuclear Physics (A2 only)

9Option: Astrophysics (A2 only)

10Option: Medical Physics (A2 only)

11Option: Engineering Physics (A2 only)

12Option: Turning Points in Physics (A2 only)

Go student ad image

Unlock your full potential with GoStudent tutoring

  • Affordable 1:1 tutoring from the comfort of your home

  • Tutors are matched to your specific learning needs

  • 30+ school subjects covered

Book a free trial lesson