Because the acceleration is always directed towards the center of the circle, it is sometimes called centripetal acceleration (向心加速度).
Period (周期) of motion:
Nonuniform circular motion—Figure 3.30
Radial and tangential components of the acceleration
Motion along a curve
where is the tangential acceleration,is the normal acceleration.is the unit vector along the tangential direction and is the unit vector along the normal direction.is the radius of curvature (曲率半径) at the point P.
is the tangential acceleration, 
is the normal acceleration.
is the unit vector along the tangential direction and 
is the unit vector along the normal direction.
is the radius of curvature (曲率半径) at the point P.
