Gravitational Fields (CIE A Level Physics)

• There is a force of attraction between all masses
  • This force is known as the ‘force due to gravity’ or the weight
• The Earth’s gravitational field is responsible for the weight of all objects on Earth
• A gravitational field is an example of a field of force and is defined as:

Force per unit mass

• The direction of the gravitational field is always towards the centre of the mass
  • Gravitational forces cannot be repulsive

Weight of person on Earth and on Jupiter

A person’s weight on Jupiter would be so large a human would be unable to fully stand up

• The direction and magnitude of a gravitational field is represented by gravitational field lines
  • Gravitational fields can be uniform or non-uniform

• Radial fields are non-uniform fields
  • The gravitational field strength g decreases with distance from the centre of the object
  • The gravitational field lines around a point mass are directed radially inwards

• Parallel field lines represent a uniform field
  
  • The gravitational field strength g is the same throughout the field
  • The gravitational field lines of a uniform field, where the field strength is the same at all points, is represented by equally spaced parallel lines
  • The Earth's gravitational field near the surface is almost uniform; therefore, it can be approximated as uniform

Gravitational field lines for a point mass and for a uniform gravitational field

Gravitational field lines for a point mass are radial and, for a uniform gravitational field, are parallel