Fig. 621.10 Falling Sticks: Six Vectors Provide Minimum Stability: A. Stick standing alone is free to fall in any direction. B. Two sticks: free to fall in any direction. C. Two sticks joined: free to fall in two directions and to slide apart at bases. D. Three sticks: free to fall in any direction. E. Three sticks joined: only free to slide apart at bases. F. Four sticks: a propped-up triangle_the prop is free to slide out. G. Five members: two triangles may collapse as with a hinge action. H. Six members: complete multidimensional stability_the tetrahedron.