Home >> Resources >> Lecture Demos >> Rolling Down A Hill

# Rolling Down A Hill

Conservation of Energy is the big physics concept behind this video even though it is not explicitly stated as such. I use this demonstration to conclude a learning session focused on moment of inertia and the kinetic energy of rolling objects. If I was to use this video with a class I would stop it at various points and ask the class leading questions but not answer them at that moment. Perhaps get them to write the answers down instead. Predict, observe, and explain. For your information here are my questions and answers.

0.10 What is the “Moment of Inertia” of an object related to? (The distribution of the mass within the object I=mr2)

0.31 Why do they have different moments of inertia? (The mass density distribution is different for both)

0.45 Which cylinder has the highest moment of inertia? (Brass on the outside) How does the moment of inertia affect the way the cylinders roll down the slope? (Both have the same initial potential energy, the one that needs the most energy to rotate E=0.5Iw2 will therefore have the least energy to translate)

From 3.36 on the concept is still the same but there is an add twist. Not all of the content of the cans rotates so the rolling kinetic energy depends only upon the moment of inertia of what is rolling.

All videos available for use under a Creative Commons Australia CC-BY-NC licence