- #1

Zheng_

- 24

- 1

## Homework Statement

I was learning how to calculate moment of inertia on Youtube, and I'm confused about when to use 1/2 mr

^{2}instead of mr

^{2}.

This video says that he used 1/2 mr

^{2}instead of mr

^{2}because the cone is solid

But in this video, while he was calculating a

**solid**sphere,

he used mr

^{2}.

Can someone explain to me why and when should I use mr

^{2}please?

## Homework Equations

I=mr

^{2}

I=mr

^{2}

## The Attempt at a Solution

Maybe it's because he was trying to calculate the solid sphere by separate it into four pieces and add them together after it? But it's still solid doesn't it?