# Rotation about fixed axis

• goldfish9776

#### goldfish9776

in this notes , the author gave that the IG is the moment of inertia calculated about an axis which is perpendicular to the page ...

moment of inertia calculated about an axis which is perpendicular to the page here means id due to Ft(tangential force) only ? not include Fn ( normal force ) ?

So , for the sum of moment about O , it's involve only moment due to Ft only ? Not include Fn ? Why ? can you explain ?

## Answers and Replies

That is for the rotational acceleration around the axis coming out or the page. The normal force will have an effect on rotational accelerations around other axes which are on the plane of the page.

That is for the rotational acceleration around the axis coming out or the page. The normal force will have an effect on rotational accelerations around other axes which are on the plane of the page.
So the total moment about M is considering only the rotational acceleration about the axis which is outside of the page(tangential acceleration)?
Why the total moment about O doesn't include the normal acceleration?