# Very basic statics question/moment of inertia

1. May 11, 2014

### encorelui2

Statics: If computing the moment of inertia about the y-axis of a triangular shape in the 2nd quadrant(not touching the x-axis); would i still use hb^3 /12

2. May 11, 2014

### SteamKing

Staff Emeritus
Yes, you would, but be careful which sides you use for 'b' and 'h'. You haven't specified which is measured along the x-axis and which is measured along the y-axis. This formula only works for right triangles, incidentally.

http://en.wikipedia.org/wiki/List_of_area_moments_of_inertia

3. May 11, 2014

### nvn

encorelui2: So far, your formula looks correct. And, it is not limited to right triangles.

It does not matter whether it touches the x axis or not. And it does not matter what quadrant it is in. It only needs to have one side coincident (collinear) with the y axis, assuming b is the horizontal width of your triangle.

4. May 11, 2014

### SteamKing

Staff Emeritus
I apologize for not posting more complete information, but the OP's formula for the moment of inertia of a triangle is indeed only applicable to right triangles. The following link gives formulas for the area properties for more general triangular shapes:

http://www.efunda.com/math/areas/triangle.cfm