13.2 : 运动方程：法向量和切向量

The motion of a particle in a curvilinear path can be described using the normal and tangential components.

The normal component is directed along the normal (or radial) path to the curve at a particular point. It depicts the variation in the trajectory of the velocity vector.

The tangential component is tangential to the curve at a specific point and characterizes the rate at which speed changes along the path.

The equation of motion for a particle in a curvilinear motion can be expressed using Newton's second law of motion along normal and tangential components.

Here, positive tangential acceleration represents an increase in the magnitude of the speed, and negative tangential acceleration represents a decrease in the magnitude of the speed of the particle.

On the other hand, the normal component of the acceleration is always along the radius of the curved path, and it is positive when directed towards the center of the curvature. The normal component of the force is also defined as centripetal force.