Consider a fly in motion. To locate its position in a three-dimensional space, a Cartesian coordinate system is used, and the unit vectors along the axis provide its direction. The vector arrow which extends from the origin to the object's location is the position vector. It can be represented in terms of the unit vectors. The position vector is the sum of the vector components on each axis and their magnitudes provide the position along each axis. If the fly continues its motion, its position vector changes, and the vector difference between the position vectors is called the displacement vector, Δr, which represents the change in position. For example, if the fly is at point A, and after time t, it reaches point B, then using the position vectors of A and B, the displacement vector of the fly for time t can be obtained.