1. Coil springs

This spring consists of a wire of generally circular cross-section wound into a cylindrical helix at a constant pitch and subjected to a force acting along the axis of the cylindrical helix or producing a force for the purpose of reproducing or modifying a movement or maintaining a system of forces in equilibrium.

The force may tend to lengthen or shorten the spring, depending on whether it's a tension or compression spring.

The helical spring can be likened to a helically wound torsion bar.

Let's consider any straight section Σ of wire, i.e. normal to the mean fiber, and G the center of gravity of this section (figure 1 ). The axis of the spring crosses the plane of the section at a point O and makes an angle...