Apply the knowledge of the circle to explain why the wheels are designed to be round?
Rolling friction is much smaller than sliding friction
This problem involves rolling friction and sliding friction. Slip friction is the friction that the object produces when sliding along the surface of another object. Rolling friction is the friction that an object produces when rolling on another object. It is much smaller than the maximum static friction and sliding friction, in general, rolling friction only sliding friction resistance of 1/40 to 1/60. So the ground animal body than pushing objects to slide much more effort. People designed the wheel, is to change the sliding friction for the rolling friction, and round objects are most conducive to rolling (round objects in the center of gravity relative to the ground contact point is the same, rolling up do not need to overcome the gravity work), so The wheel was once the greatest invention of mankind.
The so-called circle, that is, in the plane to the fixed point of the distance is equal to the set of fixed points, fixed point is the center of the circle, which can make the wheel shaft (center) to the ground the same distance, and not bumps, so to design a round.
