Gravitational Fields

• Gravitational Fields are attractive, drawn towards the centre of a point mass

  Gravitational field strength = g = F/m
• Newtons law of gravitation: The force between two masses is proportional to the product of the masses involved and inversely proportional to the square of the separation

  
  

  The gravitational force =

  F = -G * M * m/r^2
• Gravitational Field for a point mass:

  g = G * M/R^2
• In a uniform gravitational field, The field lines are:

  Equally spaced and

  Perpendicular
• Kepler's first law:

  The orbit of a planet is an ellipse with the sun being at one foci
• Kepler's second law:

  A line segment joining a planet and the sun sweeps out equal areas during equal intervals of time

  Moves faster when closer to the sun as there is a greater gravitational force
• Keplers Third law:

  The square of the orbital period of a planet is proportional to the cube of its orbital distance

  
• Geostationary Orbits:

  They have an orbital period of 24 hours in the same direction as the rotation of the earth

  They have a equatorial orbit

  They remain in the same position in the sky to a observer
• equation to learn

  
• Gravitational potential Energy, E =

  Energy = -G * M * m/r
• Gravitational potential:

  Vg = -G*M/r

  At infinity = 0
• The gravitational Potential is the work done to bring a unit mass from infinity to that point.
• Work done is the area under a force/distance graph

  
• Escape velocity =

  Gpe = KE

  G * M* m/r = 1/2 * m * (v^2)

  therefore V = square root = 1/2 m * (v^2)

  
• Gravitational field strength is the force per unit mass