The Physics Teacher
Consider a problem of sliding blocks, one stacked atop the other, resting on a friction-less table. If the bottom block is pulled horizontally, nature makes a choice: if the applied force is small, static friction between the blocks accelerates the blocks together, but with a large force the blocks slide apart. In that case, kinetic friction still forces the upper block forward but with less acceleration than the lower block. The choice, then, lies in the relative terms—what is meant by small and large? After a confusing experience during a recent exam, we’ve found a demonstration and graphical presentation that can help clarify the distinction between static and kinetic friction.
© 2009 The Physics Teacher, posted with permission
Ludwigsen, Daniel O. and Svinarich, Kathryn A., "Choose Wisely: Static or Kinetic Friction—The Power of Dimensionless Plots" (2009). Physics Publications. 4.