Rotation in Two Dimensions: Feynman's Physics Explained
Spinning motion can be described with perfect analogs of ordinary straight-line ideas. Instead of distance we use angle; instead of velocity, angular velocity; instead of force, torque; and instead of mass, a new quantity called the moment of inertia, which measures how hard it is to get something spinning. The laws look the same — we just swap the words. A key new rule is conservation of angular momentum: with no outside torque, total angular momentum stays constant.
The big idea
Rotation obeys the same laws as straight-line motion, in new words.
Think about it
Why is it harder to start a heavy merry-go-round spinning than a light one, even with the same push?
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