Friction block used for demonstrating vectors

Students often struggle to understand the independence of velocity vectors in two-dimensional motion. Despite seeing classic projectile demonstrations, it is probably not obvious to most new students why the path of motion is parabolic. Likewise, first-year students might not predict that the path of motion is linear in two-dimensional vector problems such as a boat traveling at constant velocity across a river moving at constant velocity. There do exist excellent computer simulations, but students are more likely to believe the results if they can create the motion themselves. Fortunately, students can directly explore such motion using blocks of wood that are commonly used in the classroom to measure friction. The instructor only needs to make a few inexpensive modifications to the blocks to not just teach vector motion, but with a little imagination teach many more concepts in physics. In this article I will elaborate on those modifications and uses.