Rotational Kinetic Energy
▶︎ Watch it animatedinteractive step-through · ~3 min · optionalA spinning body can sit in one place and still store energy: a flywheel can do work as it slows down. That energy is its rotational kinetic energy, K = ½ I ω². The formula is the rotational twin of ½ m v², with the moment of inertia I in place of mass and the angular speed ω in place of speed. The whole topic comes down to keeping the two apart.
The calculus here is nothing new; the care is all in the formula. The most common slip is reaching for ½ m v² (or dropping a rim speed v = ωR in for ω). Next is forgetting the square on ω or the leading ½. Third is grabbing the wrong moment of inertia for the shape. Pair I with ω, keep the ½ and the square, and pick the right I.
The work
3 ways in · any order
Lesson
Rotational Kinetic Energy
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Rotational kinetic energy, K = (1/2) I omega^2, as the rotational twin of (1/2) m v^2. Covers choosing the moment of inertia for the shape, why omega is squared, and why omega, not a stray linear speed, belongs in the rotational form. Closes with a ten-scenario skill check.
Diagnostic
10-item topic check
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Ten items across the three Topic 6.1 mistakes: using the linear formula (or a rim speed) for a spinning body, breaking the structure of (1/2) I omega^2 (dropping the half or the square), and choosing the wrong moment of inertia. Take it cold to see what still trips you up, or after the lesson to confirm it doesn't.
Targeted Practice
Drill a single misconception
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Pick one mistake you keep making and drill it on its own. Two correct in a row clears it and you move on.