A body is in static equilibrium when it is at rest and remains at rest over time. Understanding when this happens is the first step towards the study of forces: if we can write the conditions that keep a body still, we can also predict when it will instead start to move. This section starts from the simplest case, the point mass, and then extends the discussion to the rigid body, where it is no longer enough to cancel the forces, but the moments must be cancelled too.