Calculate the kinetic energy of a rotating object based on its moment of inertia and angular velocity.
Last updated: March 2026 | By ForgeCalc Engineering
Rotational kinetic energy is the energy an object possesses due to its rotation. It is the rotational analog of translational kinetic energy (1/2 m v²). Instead of mass, we use the moment of inertia (I), and instead of linear velocity, we use angular velocity (ω).
The moment of inertia represents how the mass of an object is distributed relative to the axis of rotation. An object with more mass further from the axis will have a higher moment of inertia and thus store more energy at the same rotational speed.
Where:
• K_rot is the rotational kinetic energy (J)
• I is the moment of inertia (kg·m²)
• ω (omega) is the angular velocity (rad/s)
A flywheel is a mechanical device specifically designed to store rotational kinetic energy. They are used to smooth out power delivery in engines or to store energy for later use.
To convert Revolutions Per Minute (RPM) to radians per second (rad/s), multiply by 2π and divide by 60. (ω = RPM × 2π / 60).
Yes. A rolling ball has both translational kinetic energy (from its movement across the floor) and rotational kinetic energy (from its spinning). The total energy is the sum of both.
For a solid sphere of mass M and radius R rotating about its center, the moment of inertia is I = 2/5 M R².
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