7.1 fields

• Force fields

  • A region where an object will experience a non-contact force
  • Cause interactions between objects
  • E.g. between static or moving charges
  • Any object with a mass will experience an attractive force when in the gravitational field of another object
  • Only objects with large masses have a significant effect
  • E.g. stars and planets
• Field lines

  • Force fields can be represented by vectors showing the direction of force
  • Gravitational field lines - arrows showing the direction of the force a mass would feel in a gravitational field
  • Radial field lines - field lines meet at the centre of the object
  • Lines spread out the further they get from the centre - the more spread out the weaker the force
  • Uniform field lines - field lines are parallel and equally spaced in the direction of the object
  • Force is equal at all points - lines are equally distanced
• Gravitational and electrostatic forces

  Similarities

  • Both have inverse-square force laws that have many characteristics in common
  • use of field lines
  • use of the potential concept
  • equipotential surfaces  

  Differences

  • masses always attract
  • charges may attract or repel