Keep It the Same!

I see so many students struggle with rotational motion because they overcomplicate it. That’s a mistake. The easiest and most effective way to understand rotational motion is to relate it directly to linear motion.

(I don’t use the term translational—we’ve described motion in a straight line as linear since the beginning of the year. There’s no need to switch terms and create confusion.)

The first thing I do is create a side-by-side chart comparing linear and rotational motion:

Linear	Rotational
Distance (d)	Angular Displacement (𝚹)
Velocity (v)	Angular Velocity (⍵)
Acceleration (a)	Angular Acceleration (𝛂)
Force (F)	Torque (𝝉)
Momentum (p)	Angular Momentum (L)
Mass (m)	Moment of Inertia (I)

Earlier in the year, we treated mass as a quantity. Moving forward, I want you to think of mass as resistance to change—that is, inertia. This mindset shift will help you better understand the moment of inertia, which is a rotating object’s resistance to change in motion. It’s the first time in physics we use an object’s shape to determine its behavior.

Next week, I’ll show you how the linear formulas you’ve already mastered apply to rotational motion—same ideas, just spinning.

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