Two forces, three, or more
In everyday life we constantly meet objects with various forces applied to them. A body can be in equilibrium under two such forces, three, or more.
However many forces act, the requirement is the same one — they must add up to zero. But how the forces have to be arranged to reach that zero depends on how many there are, which is why this chapter takes the cases separately.
The route through this chapter
| Section | Number of forces | Example |
|---|---|---|
| 12.2 | Two forces | A book on a table |
| 12.3 | Three parallel forces | A child sitting on a swing |
| 12.4 | Three non-parallel forces | A picture hanging on a wall |
In each of the three we begin with an activity and end with a list of the conditions the forces have to satisfy.
What equilibrium means
A body is in equilibrium when the resultant of all the forces acting on it is zero. The body then stays still.