# Archive

## Why Measure Moment of Inertia

August 12, 2020

Calculation vs Measurement The MOI of simple objects can be calculated fairly accurately using well-known formulas. To calculate the MOI for more complicated objects, you would need to model the object as a collection of simple shapes, calculate the individual MOI’s for each, and add the MOI values to obtain an aggregate value. However, when […]

## Principle of Operation of an MOI Instrument

The moment of inertia of any object can be measured through its CG by hanging the object from a wire, twisting it slightly to initiate oscillation, and timing the period of oscillation. However, anyone who has ever tried this finds that the object swings from side to side and bounces up and down rather than […]

## Torsion Pendulum Theory

Torsional Pendulum Theory Figure Consider the torsion pendulum of Figure 1 consisting of a disk of mass moment of inertia I lb-in-sec2, restrained in rotation by a wire of torsional stiffness K in-lb/radian. If the disk is turned an initial angle and sharply released, it will oscillate with damped harmonic motion as shown in Figure […]

## How to Find MOI Through CG Without Knowing the CG Location

Why measure Moment of Inertia (MOI) through the Center of Gravity (CG)? When an object is free to rotate, it will rotate around an axis passing through its center of gravity. Therefore it is essential to know moment of inertia through center of gravity to assess the flight characteristics of a payload. The MOI about […]