Hugh Beyer wrote:
Model the body as a sphere, gimballed so it turns freely in any direction. Any incoming force hits the surface of the sphere. If the force is off-center, even the slightest bit, the sphere turns and the force is deflected. If the force is dead on center, the slightest turn of the sphere moves it off center and deflects it. The force can't prevent that turning because the surface of the sphere moves perpendicular to the force, so the force can't counter it. We counter the 50-pound force not by opposing it, but by disrupting it so we never have to deal with it at all.
Taking this point further, courtesy of I Liq Chuan and its headmaster, Sam F.S. Chin:
...and a clip of a martial application based on the sphere (and spheres within the sphere...) and tangent force:
With a little stylistic tweaking of the outer expression, can y'all see the applicability to aikido throws inherent in that?