Average velocity is given as the ratio of displacement to the time interval during that displacement. In a two-dimensional space, the displacement vector, Δr, represents the change in position. If the velocity is considered at any given moment, the elapsed time approaches zero. Now, the limit of the average velocity approaches instantaneous velocity and is equal to the derivative of the position vector with respect to time. The direction of the instantaneous velocity vector at any point is always along a line tangent to the path at that point. The components of velocity in a two-dimensional space are the time derivatives of the coordinates x and y. Thus, the instantaneous velocity vector is the sum involving two unit vectors. When describing a 3-dimensional motion, the z-axis is also involved, and the velocity vector is represented using three unit vectors. In the instantaneous velocity vector, the magnitude represents the speed of the object.