Inertia Products: Solve Ixy, Iyz, Izx

  • Thread starter Thread starter unscientific
  • Start date Start date
  • Tags Tags
    Inertia
Join the discussion
Registration is free. Start your own thread to ask a follow-up.
3 replies · 1K views
unscientific
Messages
1,728
Reaction score
13

Homework Statement


http://i45.tinypic.com/hwcsy0.png

The Attempt at a Solution



I'm not sure how to find the rest; Ixy, Iyz and Izx...
Usually for integrals such as moments of inertia you will be able to reduce it to only one variable. However, there are 2 variables here; xy, yz and zx. How do i reduce it to only one?
 
Last edited by a moderator:
Physics news on Phys.org
You don't. You evaluate the triple integrals.
 
vela said:
You don't. You evaluate the triple integrals.
Are my Ixx, Iyy and Izz are correct?

Oh, so it's dM = dx dy dz,

then the range for dx is from -√(a2-y2-z2) to √(a2-y2-z2)

for dy it's from -√(a2-z2) to √(a2-z2)

for dz it's from 0 to a

Are my ranges of integration right?
 
unscientific said:
Are my Ixx, Iyy and Izz are correct?
No, they're not. You can't say ##y^2+z^2=a^2-x^2## because that's true only on the spherical part of the surface. Inside the hemisphere, it doesn't hold.

Oh, so it's dM = dx dy dz,
That's dV, not dM. You should write dM = k dV = k dx dy dz.

then the range for dx is from -√(a2-y2-z2) to √(a2-y2-z2)

for dy it's from -√(a2-z2) to √(a2-z2)

for dz it's from 0 to a

Are my ranges of integration right?
Yes.