Mechanics

Parallel Axis Theorem

Relates moment of inertia about any axis to the moment of inertia about a parallel axis through the center of mass.

Variables

I
Moment of inertia
About parallel axis
kg·m²
I_cm
Moment of inertia (CM)
About center of mass
kg·m²
M
Mass
Total mass
kg
d
Distance
Distance from CM to new axis
m

Derivation

Expanding I = ∫(r + d)²dm and using the definition of center of mass gives I = I_cm + Md².

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