Teaching momentum as a directly observable quantity

Abstract In this paper we introduce a novel method to teach momentum by using direct measurements. The basic idea is to define an ordering relation ‘more momentum than’ in hands-on collision tests. When we let two pendulum masses collide inelastically head-on we can directly observe whether two objects rest jointly or if one overruns the other. We can set up a test object with a number of mass units and, with known starting heights for a pendulum, we can also set up multiples of a unit velocity. In the collision test we can systematically increase the number of mass units of a reference pendulum with fixed unit velocity until the case, that the two masses rest jointly. By counting these momentum units we can quantify the momentum with respect to velocity and mass. Finally by analysing this measurement principle in vivid thought experiments on the impossible construction of perpetual motion machines we deduce the momentum conservation. We give examples that were tested and evaluated in high school physics classes.