Acceleration is defined as the change in velocity with time. It is a vector quantity and involves a change in magnitude or direction or both. For example, a woman is walking at 5 km/h towards the east. She stops and returns, walking at 5 km/h towards the west. Here, the woman's velocity changed due to a change in direction, though its magnitude is the same in both directions, which resulted in acceleration. Acceleration is expressed in meters per second squared and can be interpreted from the velocity versus time graph where velocity is on the y-axis and time is on the x-axis. For instance, a woman is walking on a road. At point P1, she has a velocity of v1x at time t1. And after some time at t2, her velocity is v2x at point P2. The change in her velocity is given by Δv in a time interval of Δt. Thus, the average acceleration of the woman moving from point P1 to P2 is the change in the x-component of velocity, divided by the time interval. It is also given by the slope of the line P1P2.