Does this apply to a hollow cylinder or pipe?

No, this formula (½mr²) is specifically for a solid, uniform cylinder. A thin-walled hollow cylinder instead uses I = m·r², since all its mass sits at the outer radius.

Why does moment of inertia matter for rotating parts?

It determines how much torque is needed to accelerate or decelerate a rotating object — higher moment of inertia means more torque (or more time) is needed for the same angular acceleration.

Cylinder Moment of Inertia Calculator

Calculate the moment of inertia of a solid, uniform-density cylinder rotating about its central longitudinal axis, given its mass and radius. Used in rotational dynamics, motor sizing, and flywheel design.

Inputs

Results

Moment of Inertia: 0.2 kg·m²

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Formula

I = ½ × m × r² (solid cylinder about its central axis)

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Rotational and Fluid Dynamics for Engineers

Pipe flow rate, RPM-to-linear-speed conversion, moment of inertia, natural frequency, and fluid velocity — five calculations for rotating and flowing systems.

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