This was not actually homework, but I was just trying to see if I could calculate moments of inertia and apparently, I cannot.(adsbygoogle = window.adsbygoogle || []).push({});

I'm trying to show that the moment of inertia for a sphere is (2/5)MR^2

So I started with I=(integral)(r^2)(dm)

then P=dm/dv=dm/(4pi(r^2)dr)

so dm=(4)(pi)(r^2)(P)(dr)

so I substituted into the original equation, removed constants from the integral, and substituted P for M/V=(3M/(4(pi)(R^3)))

I=12pi(M)/(4(pi)r^3)[integral]r^4 (dr)

I=(3/5)MR^2 which is wrong!

(sorry about the lack of pretty math writing)

Thanks for any help, and by the way, I'm only a high school student so my calculus knowledge is very limited (in fact, the only reason I know what integration is is because of my physics class).

**Physics Forums | Science Articles, Homework Help, Discussion**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Moment of inertia of a sphere

**Physics Forums | Science Articles, Homework Help, Discussion**