Why round? It can reduce resistance, facilitate walking and increase speed by inertia.
First of all, popular science: the distance from any point on the edge of the circle to the center of the circle is equal, that is to say, the road surface of the wheel is on the edge of the circle and the axis is on the center of the circle, so the vertical height of the center of gravity of the wheel does not change relatively during the rotation. This means that the force will not be consumed, because it needs to overcome its own gravity to raise the center of gravity and turn the wheel.
If it is a regular triangle, it is obvious that the distances from its center of gravity to three sides and three vertices are different, so in the process of rotation, in the process of turning from side down to vertex down, the center of gravity will become higher from the ground, and the generated external force will be used to overcome gravity and make the center of gravity rise, so that the triangle wheel can turn.
If the maximum force provided is not enough to pull the center of gravity farthest from the ground to the distance from the vertex to the center of gravity, then the wheel can't even turn 60 degrees; But if it is a round wheel, even if the force is a little smaller, the wheel can move at will.
So round wheels can be turned into ordinary wheels.
In ancient times, humans learned to carry heavy objects with log rollers. It is said that the ancient Egyptians used this roller to carry stones to build pyramids. This is a special flat car. The floor of the car is flat on the wheels with uniform size, so the width between the floor and the ground is the same, and the flat car can move smoothly when the wheels roll. Knowing the essence of the problem and the new goal of wheel design, we can make wheels into various shapes called "equal width curves"
The so-called equiwidth curve refers to a plane curve: no matter what direction it is clamped by two parallel lines, the distance between the two parallel lines is always the same.
Extended data
Basic structure of wheel brake:
A series of special devices used to make the outside world (mainly the road surface) exert a certain force on some parts of the car (mainly the wheels), so as to brake them to a certain extent are collectively called braking systems. Its function is: to make the moving car slow down or even stop according to the driver's requirements; Make parking stable under various road conditions (including on ramps); Keep the speed of the car downhill stable.
Only the external force acting on the car in the opposite direction to the direction of the car can make the car brake, and the magnitude of these external forces is random and uncontrollable, so a series of special devices must be installed on the car to realize the above functions.
References:
Baidu-encyclopedia wheel