How do we decide dimension of motion? Consider a particle moving along ##\hat x ## direction. This motion is known as one dimensional motion as only one coordinate i.e. x is changing with respect to time. Consider a particle having circular motion in X-Y plane. In Cartesian Coordinate system, both x and y are changing with respect to time and hence the motion is two dimensional. But in Polar coordinate system(r,θ) ,only one coordinate i.e. θ is changing with respect to time and hence the motion is one dimensional. So, does the dimension of motion depend on the coordinate system? Or, Do we always use Cartesian Coordinate system to determine the dimension of motion ?