Calculation of the Moment of Inertia

Moment of inertia is:

J= ∫ρ*dV*e^2 where:

ρ = specific mass of the material the part is made off

dV= volume element

e= distance of volume element to the axis or center you consider to compute the moment of inertia.

The integral applies to the complete body.

I am quite surprised that you could ask such a trivial question which could be solved by a simple Goggle research or a look at "eng. corner" or any other eng. helping file.

You also have the definition in ALL elementary books about mechanics.

With respect, have you any idea how much brick-dust on ones forehead hurts ? Right now, my head is sobbing in pain. The answer is about 2mg, though grammar never was my strong point.

Even for a weekend question, this is dire. Prepare for the onslaught.

N/A

"the link suddenly vanished"

I guess it's moment of inertia timed out.

Moment of Inertia is widely used in mechanics and when mass is involved it is as Nick Name advises.

In layman's terms his formula is for the sum of point masses multiplied by the square of their distances from the axis of rotation.

For a single point mass this is I = m r^2.

Keep in mind however that section moment is related and is used in, for example, beam theory. The situation is analogous to that for mass except that area is used in lieu of mass.

For a slice of area whose long side "L" is parallel to the axis or rotation I is L dT x r2. where dT is an elemental width of the slice perpendicular to the axis of rotation.

For example, for a rectangular hollow section 4 inch deep, 1 inch wide and 0.1 inch wall, when bent around its strongest axis (the one parallel to the short side), the section moment is approximately 2^2 x 1 x 0.1 - this ignores second order effects because the wall is not infinitely thin and the contribution of the long side/s - which will contribute about an additional 15% if the calculation is done properly.