Overview of key terms, equations, and skills related to rotational kinetic energy, including the difference between rotational and translational kinetic energy.

Key terms

Term (symbol)Meaning
Rotational kinetic energy (K)Kinetic energy due to rotational motion. Scalar quantity with SI units of Joules (J\text J).


EquationSymbolsMeaning in words
K=12Iω2K = \dfrac{1}{2}I\omega^2KK is rotational kinetic energy, II is rotational inertia, and ω\omega is angular velocityRotational kinetic energy is directly proportional to the rotational inertia and the square of the magnitude of the angular velocity.

Common mistakes and misconceptions

Sometimes people forget that objects can have both rotational kinetic energy and translational (linear) kinetic energy. For example, a ball that is dropped only has translational kinetic energy. However, a ball that rolls down a ramp rotates as it travels downward. The ball has rotational kinetic energy from the rotation about its axis and translational kinetic energy from its translational motion.

Learn more

For deeper explanations on this topic, see our video on rotational kinetic energy.
To check your understanding and work toward mastering these concepts, check out our exercise on comparing rotational kinetic energy for different objects.