How do I get rid of infinitesimal mass element dm?
I assume you're trying to derive the moment of inertia of a hollow sphere, but you should really be more specific when posting questions.
I am not determining the moment of inertia. I didn't specify what I was doing because I just wish to know of to solve this particularly problem. How to get rid of dm?
Your differential mass is the rate of change in the mass. It will depend on the object's density (g/cm^3, kg/m^3, etc).
In your case, you have a hollow sphere, so the mass will change in relation to the area (assuming the sphere has an infinitely small thickness). That would be g/cm^2, kg/m^2, etc.
That should allow you to change your variable to dr, the differential radius, since the volume and/or the area will depend upon the radius.
But I need the constant sigma M/A (equivalent to density) which I do not know.
Maybe Integrate? I don't really understand your problem.
I need to [tex]\int dm[/tex] for a spherical shell.
Look at the thread that started this.
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