# Rotational kinetic energy review

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 ($\text J$).

## Equations

EquationSymbolsMeaning in words
$K = \dfrac{1}{2}I\omega^2$$K$ is rotational kinetic energy, $I$ is rotational inertia, and $\omega$ 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.