Springs exert one of the most common contact forces. A spring can either push (when compressed) or pull (when stretched). FIGURE 5.4 shows the spring force, for which we use the symbol $\vec{F}{}_{\text{Sp}}$. In both cases, pushing and pulling, the tail of the force vector is placed on the particle in the force diagram.

FIGURE 5.4 The spring force.

Full Alternative Text

Although you may think of a spring as a metal coil that can be stretched or compressed, this is only one type of spring. Hold a ruler, or any other thin piece of wood or metal, by the ends and bend it slightly. It flexes. When you let go, it “springs” back to its original shape. This is just as much a spring as is a metal coil.