Rotational Kinetic Energy
Definition
The energy stored in spinning — a flywheel keeps its energy in rotation the way a moving car keeps it in straight-line motion.
Unit: joule (J)
Technical definition
KE_rot = ½Iω², where I is the moment of inertia and ω the angular velocity. A rolling object's total kinetic energy is translational plus rotational.
Example
A solid disk (I = ½MR²) of 2 kg and radius 0.1 m spinning at 20 rad/s stores ½ × 0.01 × 400 = 2 J of rotational energy.
Common confusion
Students forget the rotation term for rolling objects. A rolling ball's total kinetic energy is ½mv² + ½Iω² — ignoring the spin undercounts the energy.