The average velocity of an object cannot tell us how fast or in what direction the object was moving at any given time. To identify this, we need the velocity at a specific instant of time or the instantaneous velocity. The instantaneous velocity is the limit of the average velocity as the time interval approaches zero, or the derivative of x with respect to t. Here, the variable x is used to describe an object’s position along a one-dimensional motion. Instantaneous velocity is a vector quantity, and the symbol vx is used for instantaneous velocity along the x-direction. The sign of the instantaneous velocity is the same as the sign of Δx, as time is always considered to be positive. For example, if x increases and the motion is in the positive x-direction, it implies a positive value of instantaneous velocity. Similarly, if x decreases and the motion is in the negative x-direction, instantaneous velocity has a negative value.