Moment the inertia the cube deserve to be calculated using various equations relying on the location of the axis. Normally, there room two instances that us consider. They are;

When the axis the rotation is in ~ the centre. The formula is provided as;

## Moment that Inertia of Cube Derivation

1.

You are watching: Moment of inertia for a cube

To have the moment of inertia of a cube when its axis is passing v the center we have actually to think about a few things. We will assume the heavy cube having mass m, elevation h, width w, and depth d. Interestingly, the cube’s moment of inertia will be comparable to that of a square lamina with side about an axis v the centre. Now we will assume the area thickness of the lamina to it is in ρ. We will then take the element of the lamina with cartesian works with x, y in the aircraft to be dx dy. Now we have the right to assume its mass to it is in = ρdxdy.

When we room finding the MOI us will use ρ(x2+y2) dx dy.

Next step involves integration whereby we combine over the entire lamina. We obtain;

–-a/2∫a/2 ρ (x2+y2) dx dy = ρa4 / 6.

We will certainly then substitute the values for the massive of the lamina i m sorry is ρ =ma2.

And we obtain, ns = ma2 / 6

2. because that the 2nd instance as soon as the axis is passing through the leaf we will certainly understand just how the derivation is carried out below. First, us recall the equation for moment of inertia. It is composed as;

I = ∫ r2dm

Now because we require to uncover the MOI around an axis v the edge, we will take the z-axis.

Moving forward, we have to consider the cube to be broken down right into infinitesimally tiny masses. We have the right to then assume their sizes to it is in dy, dx, and also dz. V this we get;

dm = ρ dxdydz

Here, ρ = density.

If we look in ~ the minute of inertia formula given above we have actually r as well. That is nothing yet the street from the z-axis to mass dm. Consider the coordinates of the mass ‘dm’ to be x,y, and also z). Currently the distance ‘r’ will be;

r= √ x2 + y2

r2 = x2 + y2

Meanwhile, the worth of x,y, and also z will range from O to b follow to the size of the edges.

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We will now substitute the values that we have obtained so much in the moment of inertia equation and likewise carry the end the integration.