Examining Inelastic Collisions

In introductory physics, we talk about inelastic and elastic collisions. Generally, students are quite happy about elastic collisions because they have conservation of momentum AND conservation of energy. But if we setup a perfectly inelastic collision, the student’s dilemma is the decrease in kinetic energy after the collision. The student’s question of “where does the energy go?” generally relies upon our describing unmeasureable loss mechanisms such as deformation of the object and sound. But, that is our telling rather than letting the students discover. What if the students could perform an investigation which the they can visually see where what happens to the energy? To this end we built a collision system in which a spring is compressed during a collision and a ratchet holds the spring at maximum collision. This allows us to actually find the “lost” kinetic energy.http://opus.ipfw.edu/stu_symp2013/1037/thumbnail.jp