# 2D Moment of Inertia

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Hi guys,

I'm using Hecker's paper for 2D collision response. If I set my object's moment of inertia to low values, less than 10.0 or so, I get erratic behavior. Is that normal ? Also, should the moment of inertia be commensurate with the mass, for example, if one object has mass 1.0 and moment 50.0 and another (made of the same material) has mass 2.0 should the moment be 100.0 ?

I know this stuff isn't real and is just an approximation, I'm just looking to keep things stable.

Thanks.

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As far as I remember strange things start to happen if the inertia is too low in comparison to the mass. I used the moment of inertia of a rectangle to get an idea what value is reasonable (I = m*(l^2 + w^2)/12) but often settled for a slightly higher value since it looked more natural to me. Also looking at such a formula should answer your second question. If the dimension are the same but the mass/density increases, then the moment of inertia is proportional to the mass. If it's the same material meaning that a object that is twice as heavy will have 1.4x the linear dimensions the moment of inertia actually scales with the square of the size/mass.

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Hi,

I'm basing the moments on the rectangle formula you gave and it's working so much better. Thanks a lot.

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Rutin
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khawk
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