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Primary Force, such as gravity, chemical explosion or electromagnetic force reaction, etc. exerts its energy first to get the inertial acceleration going.
The secondary ordinary contact force changes the primary acceleration in some manner. Any change in inertial acceleration, according to the law of inertia, requires a force be exerted.
Secondary force is simply a ordinary contact force (push/pull). It creates the unique effect of weight by exerting its force, by direct contact, in succession on a body. (the floor pushes on your feet, which pushes on your leg bones, which pushes on your hip bones, et., etc.., from one end of the body to the opposite end. The amount of secondary force that the surface must exert is the "weight" of the body.
In the case of the of a body resting on the earth's surface, the secondary force (the earth's surface) obstructs the gravitational acceleration of the body with enough force to stop the body's gravitational acceleration. The amount of secondary force exerted creates the effect of weight of the body.
In an accelerating rocket the primary force is the chemical explosion reaction in the rocket engines needed to accelerate the rocket. The secondary force is the floor of the rocket pushing against the astronaut that causes him/her to accelerate with the rocket. This change in inertial acceleration causes the effect of weight to be created.
In both these cases the secondary force causes the effect of weight to be created. In both cases "real weight" is created not gravity. In the case of gravity - when no secondary force is exerted the body is weightless.
Donald Hamilton
http://novan.com/mind.htm
http://novan.com/weight.htm