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2.3.3. Flexibility and Rigidity
Nature is, on the whole, pretty floppy. It achieves rigidity in the skeletons of its structures, but mostly it finds flexibility a more useful proposition for many purposes. The human world, on the other hand, is full of rigid structures. When nature puts rigidity on the outside, as with the crab’s shell, it also limits the ability of its inhabitant to grow (in fact, the only natural shape that allows ongoing growth is the snail’s spiral shell). We are not constricted by such concerns.
When you need flatness, it is a dilemma if you also want lightness and rigidity. Nature overcomes this effect in several ways, for example when it wants to keep a leaf open. Simple curvature quickly makes a flat item more rigid. Solid veins on the underside of the leaf may hold it open. Folded ridges also work, for example where a fold down the middle also helps long thin leaves. Insect wings use all three principles for unbeatable lightness and strength.
Fig. 2.7 Achieving rigidity in a light structure
People generally design things to be rigid and unmoving, whilst nature tends to design things to bend, but not break. Rigidity in structures leads to hot spots of high internal forces and vulnerability to external forces. With careful design, the structure may be allowed to move in a way that shifts forces, safely channelling them into the ground and away from weak points. Thus earthquake-proofed buildings can move and vehicle suspension absorbs much of the bumping that plagued earlier rigid carriages. Veterinarian John Dunlop used the flexibility of a rubber hose to ease the ride of his child’s cycle and thus invented the pneumatic tyre.
As mankind continues to copy nature in our inventions, we are gradually adopting
more flexibility. For example, in the chilly future of smart weapons,
self-steering bullets use contracting tendons to change the direction of the
little nosecone to ensure the bullet hits its mark.
Other parts in this sub-section:
Other sections in this chapter: