To create a stick, we, we need to stretch.
- Think of pushing down the middle point, B, of a triangle with the two other points, A and C. locked. The stretch is between A and C, and the stick is formed between A and C.
- Think of a non-moving rod. A rubber band is tied to it, and stretched outward away from the rod. When it can't stretch any further, a small force tangential to the stretch will cause the stretched rubber band to go around the rod.
In the first case, A and C are restricted from moving, while B is forced to break the A and C apart along the A-C line.
In the second case, the rod is restricted from moving, while the rubber band is pulled and stretched away from the rod. If the rubber band is ever loose, the little nudge cannot cause the rotation.