5.4 gravitational fields

• gravitational field is a field created around any object with mass, extending all the way to infinity, but diminishing as the distance from centre of mass of the object increase
• gravitational field lines are lines of force used to map the gravitational field pattern around an object having a mass
• gravitational field strength is the gravitational force entered per unit mass at a point within a gravitational field
• gravitational potential is the work done per unit mass to bring an object from infinity to a point in the gravitational field
• point mass is a mass with negligible volume
• radial field is a symmetrical field that diminishes with distance^2 from its centre
• newtons law of gravitation is the fore between two point masses is directly proportional to he product of the masses and inversely proportional to the square of the seperation between them
• keepers first law states an orbit of a planet is in ellipse with the sun as one two foci
• aphelion is the further point from the sun in orbit
• perihelion is the closet point from the sun in orbit
• kepler second law states line segment joins a planet and sun sweeps out equal areas during interval time
• kepler third law states the square of orbital period (T) of planet is directly proportional to cube average distance (r) from the sun
• satellites orbiting earth obey Keplers third law and the centripetal force is provided by gravitational force
• uses of satellites

  • communication
  • military uses
  • research
  • weather and climate
  • gps
  • television
• polar orbit orbits the poles of the earth and has a complete view of earth over given period as earth rotates beneath oath of satellite
• polar orbits examples : mapping and resonance
• low earth orbit is a close orbit and in a very short time (less than 2 hours)
• geostationary orbits are in orbit above equator and remains above the same point as the earth rotates in the same direction
• time period for geostationary orbit is 24 hours