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## Main Question or Discussion Point

I am having considerable difficulty in finding a precise definition of g-force. My understanding is that it is the acceleration an object would undergo due to just the non-gravitational and non-electromagnetic forces acting on the object. A corollary of this is that an object experiences zero g-force, a.k.a weightlessness, if and only if the vector sum of the non-gravitational and non-electromagnetic forces acting on the object is zero.

According to Wikipedia, weightlessness "is an absence of stress and strain resulting from externally applied mechanical contact-forces, typically normal forces from floors, seats, beds, scales, and the like.".

However these two definitions are contradictory in this simple example: consider a square block acted on by exactly two forces, namely a mechanical contact-force acting on the bottom of the block pointing upward, and a mechanical contact-force acting on the top of the block pointing downward. Here the vector sum of the non-gravitational and non-electromagnetic forces acting on the object is zero, and yet there is clearly no absence of stress and strain.

So the question is: which definition is right?

According to Wikipedia, weightlessness "is an absence of stress and strain resulting from externally applied mechanical contact-forces, typically normal forces from floors, seats, beds, scales, and the like.".

However these two definitions are contradictory in this simple example: consider a square block acted on by exactly two forces, namely a mechanical contact-force acting on the bottom of the block pointing upward, and a mechanical contact-force acting on the top of the block pointing downward. Here the vector sum of the non-gravitational and non-electromagnetic forces acting on the object is zero, and yet there is clearly no absence of stress and strain.

So the question is: which definition is right?