As we all know, triangles are stable. In myths and legends, there are many three-legged animals such as the three-legged golden crow.Why are there almost no three-legged animals in nature?According to the official WeChat popular science of the Institute of Physics, Chinese Academy of Sciences,Animals are basically symmetrical, which has its own set of theoretical explanations in biology, here we only talk about mechanics.
The resistance of a triangle to deformation means that within this plane
The stability of the triangle refers more to the resistance to deformation when subjected to in-plane disturbances, while the support force of the legs is actually mainly perpendicular to the plane formed by the three legs.In this situation, what is truly stable is that "the centipede is dead but not stiff".
If you have ever ridden a tricycle, you will find that it is not easy to balance the tricycle, and it can even easily roll over. A three-legged stool is also far less stable than a four-legged stool.
To take a step back,Strictly speaking, a tripod is just three non-collinear points. There are no edges connecting the three points and they cannot form a triangle.——The components of a triangle include three angles and three sides. In terms of stability alone, such three points are not as stable as a real triangle.
Three legs does not hold true in terms of stability. In fact, it is also difficult to hold true in terms of movement patterns.. You know, for animals living in nature, the most important thing is not how stable they are when standing, but their ability to move while hunting is also important.
For bipeds, the main modes are human-like running and kangaroo-like jumping. For quadrupeds, there are four main modes of locomotion, such as a horse-like trot.
But as the saying goes, two monks carry water to drink, and three monks have no water to drink.It is difficult to have a movement pattern that fully utilizes three legs.Biological evolution is stingy and cannot allow the existence of a huge limb that only plays an occasional supporting role. Otherwise, the tail can actually be regarded as a third leg.