3.7.2 Gravitational Fields

3.7.2 Gravitational Fields

1. Newton's Law

   • attractive force acting between all matter
   • magnitude of force between two point masses: F = GmM / rr
     • G is gravitational constant
     • inverse square law

2. Gravitational field strength

   • field lines
     • more dense lines means stronger field strength
     • radial (planet) - wheel spokes
     • uniform (ground level) - parallel
   • g = F / m
     • force per unit mass
   • magnitude of gravitational field strength in a radial field, g = GM / rr

3. Gravitational potential

   • V at a point is the work done per unit mass to move a small object from infinity to that point
   • V = W / m
   • defined as zero at infinity
     • negative sign
   • ΔW = mΔV
   • no work is done when moving along an equipotential surface
   • V (radial field) = - GM / r
   • g = - ΔV / Δr
     • area under graph of g against r is ΔV

4. Orbits of planets and satellites