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Mass of a Region

Here are some applications of the triple Infinite Sum Theorem. Perhaps the simplest physical interpretation of the triple integral is mass as the triple integral of density.

DEFINITION

The mass of an object filling a solid region E with continuous density ρ(x, y, z) is

12_multiple_integrals-349.gif

JUSTIFICATION

At every point of an element of volume ΔE the density is infinitely close to ρ(x, y. z), so the element of mass is

Δm ≈ ρ(x, y, z) ΔV (compared to ΔV). (See Figure 12.6.8.) By the Infinite Sum Theorem,

12_multiple_integrals-350.gif

12_multiple_integrals-351.gif

Figure 12.6.8


Last Update: 2010-11-25