how can we find dm and sigma of any given geometrical object - Physics - System Of Particles And Rotational Motion

Question

how can we find dm and sigma of any given geometrical
object?

Neha Gupta · Accepted Answer

dm is the mass of small element of the gematerical object
for two dimensonal object, mass per unit area is called surface mass density
σ = mass of the objectarea of the object = MAmass of the small element is given by:dm = surface mass density  area of the small elementdm = σ(dA)

how can we find dm and sigma of any given geometrical object?