The work done by a pendulum is difficult to calculate as the force which acts on it varies constantly.

If you select Table and start the animation you will be able to see the value of the force acting on the pendulum at many instants.

If you click on "Calculate work", you will get another window in which you will see how you can calculate graphically the area under the graph of F (x).
The calculation of the area between the graph and the x axis is done by adding up the area of small rectangles. This procedure constitutes the basis of the calculation of the integral.

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