MASSPROP

Calculates the mass properties of regions or 3D solids.

Ribbon: Tools tabInquiry panelMass Properties. Not available on the ribbon in the current workspace
Toolbar: Inquiry
Menu: Tools  Inquiry  Region/Mass PropertiesAt the Command prompt, enter massprop.
Command entry: massprop

Select objects: Use an object selection method

If you select multiple regions, only those that are coplanar with the first selected region are accepted.

MASSPROP displays the mass properties in the text window, and then asks if you want to write the mass properties to a text file.

Write analysis to a file? <N>: Enter y or n, or press Enter

If you enter y, MASSPROP prompts you to enter a file name. The default extension for the file is .mpr, but it is a text file that can be opened with any text editor.

The properties that MASSPROP displays depend on whether the selected objects are regions, and whether the selected regions are coplanar with the XY plane of the current user coordinate system (UCS), or solids. For a list of the parameters that control the MASSPROP units, see Calculations Based on the Current UCS.

Regions

The following table shows the mass properties that are displayed for all regions.

Mass properties for all regions

Mass property

Description

Area

The surface area of solids or the enclosed area of regions.

Perimeter

The total length of the inside and outside loops of a region. The perimeter of a solid is not calculated.

Bounding box

The two coordinates that define the bounding box. For regions that are coplanar with the XY plane of the current user coordinate system, the bounding box is defined by the diagonally opposite corners of a rectangle that encloses the region. For regions that are not coplanar with the XY plane of the current UCS, the bounding box is defined by the diagonally opposite corners of a 3D box that encloses the region.

Centroid

A 2D or 3D coordinate that is the center of area for regions. For regions that are coplanar with the XY plane of the current UCS, this coordinate is a 2D point. For regions that are not coplanar with the XY plane of the current UCS, this coordinate is a 3D point.

If the regions are coplanar with the XY plane of the current UCS, the additional properties shown in the following table are displayed.

Additional mass properties for coplanar regions

Mass property

Description

Moments of inertia

A value used when computing the distributed loads, such as fluid pressure on a plate, or when calculating the forces inside a bending or twisting beam. The formula for determining area moments of inertia is

The area moments of inertia has units of distance to the fourth power.

Products of inertia

Property used to determine the forces causing the motion of an object. It is always calculated with respect to two orthogonal planes. The formula for product of inertia for the YZ plane and XZ plane is

product_of_inertiaYZ,XZ = mass * distcentroid_to_YZ * distcentroid_to_XZ

This XY value is expressed in mass units times the length squared.

Another way of indicating the moments of inertia of a solid. The formula for the radii of gyration is

Radii of gyration are expressed in distance units.

Principal moments and X,Y,Z directions about centroid

Calculations that are derived from the products of inertia and that have the same unit values. The moment of inertia is highest through a certain axis at the centroid of an object. The moment of inertia is lowest through the second axis that is normal to the first axis and that also passes through the centroid. A third value included in the results is somewhere between the high and low values.

Solids

The following table shows the mass properties that are displayed for solids.

Mass properties for solids

Mass property

Description

Mass

The measure of inertia of a body. Because a density of one is used, mass and volume have the same value.

Volume

The amount of 3D space that a solid encloses.

Bounding box

The diagonally opposite corners of a 3D box that encloses the solid.

Centroid

A 3D point that is the center of mass for solids. A solid of uniform density is assumed.

Moments of inertia

The mass moments of inertia, which is used when computing the force required to rotate an object about a given axis, such as a wheel rotating about an axle. The formula for mass moments of inertia is

Mass moments of inertia unit is mass (grams or slugs) times the distance squared.

Products of inertia

Property used to determine the forces causing the motion of an object. It is always calculated with respect to two orthogonal planes. The formula for product of inertia for the YZ plane and XZ plane is

product_of_inertiaYZ,XZ = mass * distcentroid_to_YZ * distcentroid_to_XZ

This XY value is expressed in mass units times the length squared.

Another way of indicating the moments of inertia of a solid. The formula for the radii of gyration is

Radii of gyration are expressed in distance units.

Principal moments and X,Y,Z directions about centroid

Calculations that are derived from the products of inertia and that have the same unit values. The moment of inertia is highest through a certain axis at the centroid of an object. The moment of inertia is lowest through the second axis that is normal to the first axis and that also passes through the centroid. A third value included in the results is somewhere between the high and low values.

Calculations Based on the Current UCS

The following table shows the parameters that control the units in which mass properties are calculated.

Parameters that control MASSPROP units

Parameter

Used to calculate

DENSITY

Mass of solids

LENGTH

Volume of solids

LENGTH*LENGTH

Area of regions and surface area of solids

LENGTH*LENGTH*LENGTH

Bounding box, radii of gyration, centroid, and perimeter

DENSITY*LENGTH*LENGTH

Moments of inertia, products of inertia, and principal moments