Rolling Motion

Overview of Rolling Motion Problems

Rolling motion can seem really complicated in lecture, but in this video we go over some of the steps that all these problems have and talk about how these problems are different from old "stuff going down ramps" problems. I also explain one of the weird ways these problems can be done: by treating the contact point as the axis of rotation instead of, you know, the axis of the rolling object.

Energy of Cylinder Rolling on Flat Ground

In this video we calculate the energy of a rolling cylinder two ways. In the first way, we add up the kinetic energy due to the wheel's movement across the ground and the energy of the rotation. The second time we do it we do it the crazy way, treating the wheel like an object that is rotating not about its center but about the bottom of the wheel where it's touching the ground.

Acceleration of Sphere Rolling Down Hill

This is the hardest problem about rolling, where we step back into torques to try and figure out how fast a sphere accelerates as it rolls down a ramp. You're going to be wishing you could use energy on this one by the time we're done!

Velocity of a Sphere At Bottom of Hill

Ah yes, now we're back to using energy as a shortcut to solve problems that would be annoying bummers if we had to use kinematics on them.

Hoop vs Solid Disk Rolling Down a Hill of Height h

This one is kind of interesting and almost every class covers it in some way, either in lecture or homework. The question: If you roll a hoop and a disk down the same hill, which goes faster? Whether they weigh the same or one is big and one is small, the answer is the same: the winner is...

Height to Strike Billiard Ball For No Slippage

This problem still haunts me from my freshman physics class at Stanford. It was the last problem on the exam, and nobody got it right, including me! But now, applying everything we've learned in the videos up until now, it turns out to not be so bad: just set up your free body diagram, set up your net force and net torque equations, and look for stuff to cancel out.