Center of mass

The center of mass is the average position of all the parts of a system, weighted according to their masses. One useful application of knowing the center of mass is to determine the maximum angle that an object can be tilted before it falls over.

The Center of Mass command displays the location of both the original and displaced center of mass and the displacement vector, and is available for the following studies:

• Linear static stress
• Nonlinear static stress
• Thermal stress
• Dynamic event simulation
• Quasi-static event simulation

For simple rigid objects with uniform density, the center of mass is at the centroid.

Figure 1: Center of mass at the centroid for simple shapes

For more complex, oddly-shaped objects, the center of mass is the point where the weighted position vectors of all the parts of a system sum up to zero. For the purposes of calculation, an oddly-shaped object is treated as if all its mass is concentrated in a zero volume point at its center of mass. This theoretical object is the point mass.

If a force pushes on a rigid object at its center of mass, then the object always moves as if it is a point mass. It does not rotate about any axis, regardless of its actual shape. If the object is subjected to an unbalanced force at some other point, however, then it rotates about the center of mass.