Why does a spring want to come back to the original position it started at? — JF, Hazen, ND
When you stretch or bend a spring, you are displacing atoms within the crystals that make up that spring. Each atom in those crystals moves a tiny bit nearer or farther from its neighbors and it begins to experience tiny forces that would push it back toward its original position if you let go of the spring. When you do let go of the spring, these tiny forces act together to return the spring to its original shape while returning the individual atoms in the crystals back to their original positions. However, if you bend a spring too far, the atoms begin to slide across one another and they can no longer find their way back to their original positions. In that case, the spring has become permanent bent and won’t return to its original shape when you let go. Good spring materials are those that can tolerate a substantial amount of stretching or bending without allowing their atoms to slide across one another. Many common metals don’t make good springs because this sliding occurs much too easily.