a level physics

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  1. a gravitational field is
    a region where any other mass will experience a force
  2. the gravitational field strength , g , at a point us defined as the
    • force that acts on a unit mass placed at that point 
    • g = F/m 
    • units Nkg-1
    • vector quantity
  3. a gravitational field can be represented by
    • sketching field lines around a mass 
    • the field lines show the direction of force that acts on another mass
  4. near the earths surface the field lines are approx
    parallel to each other and perpendicular to the surface of the earth , the field is said to be uniform - the gravitational field strength is the same magnitude and direction throughout the field
  5. on a larger scale the field lines around a spherical mass
    spread out radially
  6. force of gravity on a small mass near a much larger spherical mass is always directed to
    the centre of the larger mass
  7. the magnitude of g in a radial field .... with increased distance from the massive body
  8. over small distances which are much less than the earths radius the change in gravitational field strength is
    insignificant so the field is considered to be uniform
  9. for a radial field such as that due to a spherical mass , M , the force that acts on a small mass , m , placed at distance , r, is given by Newtons law as
    F = GMm/r2
  10. g = F/m therefor g also =
    • g = GMm/mr2
    • so 
    • g = GM/rr
  11. inside the earth as r becomes smaller the mass becomes smaller so g
  12. draw a graph to show how g changes with r
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a level physics
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