Two arrangements to come
Forces can be applied to an object in all sorts of directions. So the cases have to be separated by arrangement.
Forces with the same line of action. Both act along one and the same straight line.
Section 9.2.
Forces that are parallel but have different lines of action. One direction, two lines.
Section 9.3.
Collinear forces split again
Two forces acting along one line still leave a choice — do they go the same way, or against each other? Section 9.2 looks at both separately, because the two answers are different.
| Section | Arrangement | Resultant |
|---|---|---|
| 9.2 | Collinear, same direction | The sum |
| 9.2 | Collinear, opposite directions | The difference |
| 9.3 | Parallel, same direction | The sum |
| 9.4 | Inclined | Direction between the two |
That table is the map of the whole chapter. The four sections ahead do nothing but establish one of its rows each, with an activity and a worked example.