Physics A2 Level

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Physics A2 Level
2011-12-22 07:28:19
physics alevel gravitational fields

Gravitational Fields
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  1. Newton's law of gravitation
    • Assumes that the gravitational force between any two point objects is: always an attractive force, proportional to the mass of each object and proportional to 1/r2 (r is distance apart)
    • gravity is a universal force acting between all mater
  2. Gravitational field strength
    • force field: a region in which a body experiences a force
    • Radial field: field lines are like spokes on a wheel, directed towards the centre
    • Uniform field: field lines are parallel and equally spaced
    • g=F/m
    • In a radial field g=GM/r2
  3. Gravitational potential
    • the gravitational potential at a point in a gravitational field is the gpe per unit mass of a small test mass. It is equal to the work done per unit mass to move a small object from infinity to that point as the gravitational potential at infinity is zero
    • work done in moving mass: W=mV
    • V in a radial field: V=-GM/r
    • gravitational field strength is the negative of the potential gradient: g=-V/r
  4. Orbits of planets and satellites
    • v=square root (GM/r)
    • T=square root(4pi2r3/GM)
    • A satellite's total energy is constant, so kinetic and potential energy is also constant (KE + PE = TE)
    • Geosynchronous orbit: always above the same point on Earth, same angular speed as the Earth