Math Problem Statement

How to calculate the center of mass and total mass for a 3D object with a density function \( \rho(x, y, z) \)?

Solution

The image contains mathematical formulas related to calculating the center of mass of a three-dimensional object with a given density function ρ(x,y,z)\rho(x, y, z). Here is a detailed breakdown of the provided formulas:


  1. Total Mass of the Object: The mass MM of the volume VV is given by the triple integral: M=Vρ(x,y,z)dxdydzM = \iiint_V \rho(x, y, z) \, dx \, dy \, dz

    This computes the total mass by integrating the density function ρ(x,y,z)\rho(x, y, z) over the entire volume VV.


  1. Center of Mass Formulas: The coordinates of the center of mass (xˉ,yˉ,zˉ)(\bar{x}, \bar{y}, \bar{z}) are defined as: xˉ=1MVxρ(x,y,z)dxdydz\bar{x} = \frac{1}{M} \iiint_V x \, \rho(x, y, z) \, dx \, dy \, dz yˉ=1MVyρ(x,y,z)dxdydz\bar{y} = \frac{1}{M} \iiint_V y \, \rho(x, y, z) \, dx \, dy \, dz zˉ=1MVzρ(x,y,z)dxdydz\bar{z} = \frac{1}{M} \iiint_V z \, \rho(x, y, z) \, dx \, dy \, dz

    • xˉ\bar{x}: Weighted average of xx values over the volume, with ρ(x,y,z)\rho(x, y, z) acting as the weight.
    • yˉ\bar{y}: Weighted average of yy values.
    • zˉ\bar{z}: Weighted average of zz values.

  1. Summary:
    • V\iiint_V: Denotes a triple integral over the 3D volume VV.
    • dxdydzdx \, dy \, dz: Differential volume element in Cartesian coordinates.
    • The density function ρ(x,y,z)\rho(x, y, z) determines how the mass is distributed throughout the volume.

Do you need a worked-out example or further clarifications on these formulas?

Here are some questions to expand the discussion:

  1. What is the physical interpretation of the center of mass in a system?
  2. How do the formulas change if the density ρ\rho is constant?
  3. Can these formulas be applied in cylindrical or spherical coordinates? How?
  4. What are some practical applications of these formulas in engineering or physics?
  5. How would you set up these integrals for a specific volume, such as a sphere or a cube?

Tip:

To simplify computation, exploit symmetry in ρ(x,y,z)\rho(x, y, z) or VV when calculating the center of mass. Symmetry can often make some terms of the integral equal to zero.

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Math Problem Analysis

Mathematical Concepts

Triple Integrals
Center of Mass
Density Function
Multivariable Calculus

Formulas

M = \iiint_V \rho(x, y, z) \, dx \, dy \, dz
\bar{x} = \frac{1}{M} \iiint_V x \rho(x, y, z) \, dx \, dy \, dz
\bar{y} = \frac{1}{M} \iiint_V y \rho(x, y, z) \, dx \, dy \, dz
\bar{z} = \frac{1}{M} \iiint_V z \rho(x, y, z) \, dx \, dy \, dz

Theorems

Center of Mass Formulas for Continuous Mass Distribution

Suitable Grade Level

Undergraduate Level (Calculus II/III or Multivariable Calculus)