Hi Wiz,
Because we've all spent a lifetime experiencing what 1g feels like, measuring weights using spring balances, predicting the flight of tennis, squash, foot balls etc. - we reckon we can tell which acceleration is due to gravity. If we measure or notice a difference with respect to the reference frame of planet earth (e.g. looking out of the window or Artificial Horizon in IMC (same as lift shaft with no windows))- then it must be due to some other acceleration.
Last edited by rudderrudderrat; 9th Jul 2010 at 11:03.