Gravitational Fields

Gravitational Fields

1. Field Patterns

   • radial field
     • field lines directed to centre
     • Earth
   • uniform field
     • gravitational field strength is the same in magnitude and direction throughout the field
     • field lines are parallel and equally spaced

2. Gravitational potential

   • potential energy
     • energy of an object due to its position in a gravitational field
     • position for zero GPE is at infinity
   • potential gradients
     • Equipotentials
       • lines of constant potential
       • lines get further apart at increasing distance form Earth's surface
       • closer equipotentials are
         • greater the potential gradient
       • lines of equal spacing
         • potential gradient is constant
           • gravitational field strength is constant
             • uniform field
       • direction of the lines of force of the gravitational field are always perpendicular to the equipotentials
     • change of potential per metre at that point
   • GPE per unit mass of a small test mass
     • work done per unit mass to move a small object from infinity to that point

3. Newton's law

   • assumes that the gravitational force between any two point objects is
     • always an attractive force
     • proportional to 1/r^2
       • r is the distance apart
   • force of gravity
     • vector
     • depends on masses involved and distances between them
   • inverse square law

4. Satellite motion

   • geostationary satellites
     • orbits Earth directly above the equator
       • time period of 24 h
     • remain in a fixed position above the equator
   • kept in orbit by the gravitational pull of the Earth