Identify reasons for possible variations from the value of 9.80665 m/s2

The value for the gravitational acceleration on Earth's surface mainly have to do with geographical location. The factors that cause these are:

  • Composition and structure of the ground
    • The composition of the Earth's lithosphere is not constant.
    • As greater mass creates a stronger gravitational field, the gravitational force would be STRONGER where the soil is DENSER.
  • The shape of the planet.
    • The Earth is NOT a perfect sphere, rather it is an ELLIPSOID.
    • It is flatter at the poles and bulged out at the equator.
    • As gravitational force is affected by distance ($F_g = \frac{GMm}{r^2}$) the CLOSER one is to the Earth the STRONGER the gravitational force.
    • Thus, gravitational acceleration is:
      • GREATER ($9.83ms^{-2}$) at the POLES
      • LESSER ($9.78ms^{-2}$) at the EQUATOR
  • Earth's rotation
    • The spin of the Earth can reduce the effective gravitational force due to a centrifuge effect as some of the weight force actually provides the centripetal force for the Earth to rotate.
    • As the Earth effectly doesn't spin at the poles and spins the fastest at the equator, gravitational acceleration is:
      • GREATER ($9.83ms^{-2}$) at the POLES
      • LESSER ($9.78ms^{-2}$) at the EQUATOR
  • Altitude
    • As said before, the distance from the centre of mass effects the gravitational force and subsequently the gravitational acceleration at that point.
    • From that, Altitude will obviously affect the gravitational acceleration in some way.
    • A body that is x metres above the planet will undergo the gravitational acceleration of $g = \frac{GM}{(r+h)^2}$ (This is talked about in the next dot point.)
    • Thus, the HIGHER the altitude, the LESSER the gravitational acceleration.