If  the speed  of the  particle  in  circle  varies, it  is ${\alpha }_r$ example of non-uniform circular motion A roller  coaster  car that  slows  down  and speeds up as it  moves around  vertical  loop. The radial  component of acceleration  ${\text{α}}_{\text{r}}\text{=}\frac{{\text{v}}^{\text{2}}}{\text{r}}$ which is perpendicular  to the  instantaneous velocity  still  acts and is directed  towards  the center of the circle  . Since  speed  has different  value at different  points  in the motion, the value  of ${\alpha }_{r\alpha d}$ is not  constant. Radial acceleration  is greatest  at the point  in the  circle  where  the speed  is greatest. In  non- uniform circular  motion there is also  a component  of the acceleration  that is parallel to the  instantaneous  velocity  This  is the  component ${\alpha }_{\left|\right|}or{\alpha }_{\tan gential}$.i.e  tangent  to the circle , ${\text{α}}_{\text{tangential}}$ is equal  to rate  of change  of  speed  . Thus  ${\text{α}}_{\text{rad}}\text{=}\frac{{\text{v}}^{\text{2}}}{\text{r}}{\text{andα}}_{\text{tangential}}\text{=}\frac{\text{d}\left|\text{v}\right|}{\text{dt}}$.