The force-reduction generator

A force may be moved anywhere, at the price of a couple. A 60 kN force applied 180 mm off the centreline of a body, and the same force applied ON the centreline together with a couple of 10.8 kNm. The two systems are equivalent: they have the same resultant force and the same moment about every point in space, so no equilibrium equation written about the body can tell them apart. What they are not is the same loading — the stresses inside the body differ, and they differ over a distance of about the body's own depth. The offset is drawn to a scale that keeps the arrow on the body; the number beside it is the real one.

1 essay calls force-reduction. The drawing above is what it returns with no arguments at all; every call below passes it something, because a placement that passes nothing draws whichever member of the family the generator happens to default to rather than the one its essay argues about.