2. Curvature of the curve. The curvature of a plane curve is defined by the differential of the rotation rate of the tangent direction angle to the arc length at a certain point on the curve, which indicates the degree to which the curve deviates from the straight line.

3.K = lim | δ α/δ s |, and when δ s tends to 0, k is defined as curvature.

4. Curvature radius is mainly used to describe the degree of curve bending change somewhere on the curve. Special examples are: the curvature of a circle is the same everywhere, and the radius of curvature is its own radius; The straight line does not bend, so the curvature is 0, and 0 has no reciprocal, so the straight line has no radius of curvature.

5. The bigger the circle, the smaller the bending degree and the closer it is to a straight line. So the bigger the circle, the smaller the curvature, the smaller the curvature and the larger the radius of curvature.

6. If a relative circle with equal curvature can be found at a certain point on the curve, then the radius of curvature at that point on the curve is the radius of the circle.