When a particle moves along a curved trajectory, its motion can be described using tangential and normal components. Both the components are attached to the particle and move with it. For the n-axis, the curved path of the particle is split into multiple different arc segments. Each segment forms the arc of a circle having a radius of curvature and a center of curvature. The n-axis is normal to the t-axis, and its positive sense points towards the center of the curvature, defined with unit vector un. The positive of the t-axis is defined along the increasing position of the particle on the path, and it is denoted using a unit vector, ut. The particle's velocity is always tangent to the path of the curvilinear motion and has only a t-component. Differentiating velocity expression with time gives the acceleration of the particle. Here, ut changes at each instant, and its change denotes the direction of un. This means that for curvilinear motion, the acceleration of the particle has both tangential and normal components