A car moving at variable speed is under the influence of a variable force. To find the work done by the force in moving the car from point A to B, the one-dimensional varying force with the distance covered by the car is plotted. The area under the curve is divided into a number of strips of discrete width. For each strip, the applied force is approximately constant. So, the work done by the variable force for the total distance between A and B is given by the sum of the individual work done by the constant force for the small segments. For better approximation, increase the number of strips such that the width of each strip approaches zero. So, the work done can be given by the integral of the one-dimensional varying force with respect to the distance, and represented as the area under the curve. Using Newton's second law and applying the chain rule of calculus, the work done can be rewritten in terms of the change in kinetic energy which is the work-energy theorem.