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.