Parallel-Axis Theorem
Reference from the original Physics I textbook.
- Parallel-Axis Theorem
The parallel-axis theorem states I = I_CM + Md², where the two axes are parallel, I_CM is about the axis through the center of mass, and d is their perpendicular separation.
- Related Glossary Terms
Moment of Inertia↗, Moment of Inertia Equation, Parallel Axis Theorem Equation
- Index
Reviewed physics notes (1)
These corrections keep the original lesson’s purpose while fixing errors in the source edition.
- Original omits the parallel condition and center-of-mass requirement. — Reference 1
Glossary and deeper reading · 2 refreshers
These editorial refreshers supplement the reading. Definitions and examples are added guidance; original source wording and recorded answers remain in their original context.
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Parallel-axis theorem
The parallel-axis theorem relates rotational inertia about a center-of-mass axis to inertia about a parallel displaced axis. The displaced-axis value is the center-of-mass value plus total mass times the squared separation of the axes. For example, a uniform rod has greater rotational inertia about one end than about a parallel axis through its middle.
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Rotational inertia
Rotational inertia measures how strongly a mass distribution resists a change in angular velocity about a specified axis. Mass farther from that axis contributes more strongly because each contribution depends on squared distance. For example, moving small masses outward along a rotating rod increases its rotational inertia without changing its total mass.