Spring not showing Hooke's Law behavior with low forces

Springs may not show linear behavior at low force levels

Springs that do not show air space between each of the turns of the spring will have residual compressive stresses between the turns of the spring.  The spring will not show Hooke's Law behavior until all of the turns of the spring show some space between them.  Please instruct your students not to collect or to discard data prior to visible air spaces appearing between the turns of the spring.