This, then, means that the average force acting throughout the stroke is 3 pounds, and the total work done is 3 × 10 = 30 foot-pounds.
Fig. 5. Work Diagram when Pressure drops Uniformly
In [Fig. 5] the pressure drops uniformly from 5 pounds at the beginning to 0 at the end of the stroke. In this case also the area and work done are found by multiplying the length of the diagram by the average height, as follows:
| 5 + 0 | |
| ——— | × 10 = 25 square feet, |
| 2 |
or 25 foot-pounds of work done.
The object of [Figs. 3], [4] and [5] is to show how foot-pounds of work may be represented graphically by the areas of diagrams, and also to make it clear that this remains true whatever the form of the diagram. It is also evident that knowing the area, the average height or pressure may be found by dividing by the length, and vice versa.
