Mechanics
Moment of Inertia (Point Mass)
Rotational equivalent of mass for a point mass.
Variables
Ikg·m²
Moment of inertia
Rotational inertia
Allowed values: 0 or more
mkg
Mass
Point mass
Allowed values: 0 or more
rm
Distance
Distance from axis
Allowed values: 0 or more
Derivation
Definition: I = Σmᵢrᵢ² for discrete masses.
Your notes
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Check value
Round inputs run through this page's calculator. Use it to test your own working or a rearranged form. It is a test case, not a real-world example.
- m = 2 kg (Mass)
- r = 3 m (Distance)
Result: I = 18 kg·m²
Other mechanics formulas with the same quantities
- Rolling Kinetic Energy (Rotational Motion) shares Mass, Moment of inertia
- Centripetal Force (Rotational Motion) shares Mass
- Angular Momentum (Rotational Motion) shares Moment of inertia
- Moment of Inertia (Disk/Cylinder) (Rotational Motion) shares Moment of inertia
- Moment of Inertia (Solid Sphere) (Rotational Motion) shares Moment of inertia
- Moment of Inertia (Rod, Center) (Rotational Motion) shares Moment of inertia
Where this formula is listed
- Mechanics formulas, under Rotational Motion, alongside Angular Velocity, Angular Acceleration, Linear-Angular Velocity Relation, Centripetal Acceleration and Torque.
- In the mechanics list it comes after Torque and before Newton's Second Law (Rotation).
- Mechanics formula sheet, one of 58 formulas printed with symbol keys and SI units.
- The full formula index, grouped by category and topic.
Common questions
What is the Moment of Inertia (Point Mass) formula?
Moment of Inertia (Point Mass) is written I = mr². Rotational equivalent of mass for a point mass. It belongs to Mechanics, under Rotational Motion.
What are the units in I = mr²?
In SI units, I is moment of inertia, measured in kg·m²; m is mass, measured in kg; r is distance, measured in m.
How is the Moment of Inertia (Point Mass) formula derived?
Definition: I = Σmᵢrᵢ² for discrete masses. The result is I = mr².