Gravity is an acceleration also.
Well, it is, and I think that's the point being made. There are two phenomena (for lack of a better word) acting on things - acceleration and gravity. The discussion is about frames of reference; it is not about forces.
I can understand FCeng84's point that gravity is not a "force" per se and acceleration is but the difference is confined to the results of "acceleration" (in all its forms, either gravity, as FCeng84 states) or acceleration through engine thrust, etc. The effects of gravity are felt-seen when something is unable to resist the standard acceleration of gravity.
But an aircraft in stable, level, non-accelerating flight and all it's attachments and contents are still under the effects of gravitational "force", (albeit slightly smaller at cruise altitudes). The machine and contents have "weight", against which the wings provide lift, "resisting" the effects of gravity.
So unless I'm missing something, FCeng84 is incorrect.
Fascinating.
Last edited by PJ2; 9th May 2013 at 23:39.