Physical Property Analysis

Physical PropertiesA physical property is a property that can be observed or measured without changing the identity of the matter.

Examples of Physical Properties:Volume Density Color Surface Area Centroid Moment of InertiaMass Odor TemperatureMelting Point Viscosity Electric Charge

Physical Property AnalysisThe size, volume, surface area, and other properties associated with a solid model are often part of the design constraints or solution criteria.The following are physical properties presented in typical solid modeling programs:Volume Density MassSurface Area Center of Gravity Moment of InertiaProduct of Inertia Radii of Gyration Principal AxesPrincipal Moments Length

Physical Properties

• Volume• Surface Area • Density• Mass

In this lesson you will investigate the following physical properties:

Volume

• Volume is the amount of three-dimensional space occupied by an object or enclosed within a container

• Design engineers use volume to determine the amount of material needed to produce a part

• Different formulas for different shapes

V = H x W x LV = 4” x 4” x 8”V = 128 in.3

84

4

Rectangular Prism

Volume in Cubic Units

It is imperative to keep your units the same when measuring and calculating volume.

• Cubic inches (in.3)• Cubic feet (ft3)• Cubic yards (yds3)• Cubic centimeters

(cm3)• Cubic meters (m3)

Measure volume using cubic units:

Volume Formulas for Prisms, Cylinders, Pyramids, or Cones

If B is the area of the base of a prism, cylinder, pyramid, or cone and H is the height of the solid, then the formula for the volume is

V = BHNote: You will need to calculate the area of the shape for the base of the prism. For example: If the solid is a triangular prism, then you will need to calculate the area of the triangle for the base and then calculate the volume.

Area Formulas for Bases of Prisms, Cylinders, and Pyramids

Rectangular Prism – base is rectangle, therefore A = length * width or A = lw

Cylinder – base is a circle, therefore A = pi * radius of circle squared or A = πr2

Square Pyramid – base is a square, therefore A = length * width or A = lw or side squared since the sides are the same on a square or A = s2

Volume of a ConeA Special Case

• A cone is 1/3 of a cylinder• The base of a cylinder is a circle• The area of a circle is A=πr2

• Therefore, the formula for the volume of a cone is

V= 1/3Ahwhere A=πr2

and h is the height of the cone

Density• Density is defined as mass per unit

volume.• Density is different for every material and

can be found in a machinist handbook.

Mass

• Mass is the amount of matter in an object or the quantity of the inertia of the object.

• Many materials are purchased by weight; to find weight, you need to know the mass.

Mass = Volume x Density

Using the volume from the previous example:V = 128 in.3

Mass = 128 in.3 x .035 lb/in.3

Mass = 4.48 lb

Polypropylene has a density of .035 lb/in.3 and

Surface Area

• Surface area is the squared dimensions of the exterior surface.

• Surface area is important when determining coatings and heat transfer of a part.

B

C

D

E

FA

A= 4in. x 4in. = 16 in.2

B= 4in. x 8in. = 32 in.2

C= 4in. x 8in. = 32 in.2

D= 4in. x 8in. = 32 in.2

E= 4in. x 8in. = 32 in.2

F= 4in. x 4in. = 16 in.2

A + B+ C + D+ E + F = 160 in.2

To start the Mass Property function, right click the solid model name in the Browser.

Pick Properties

Mass Property values will be used for predicting material quantity needed for production, finishing, packaging, and shipping.

Additional Physical Properties

Center of Gravity

• A 3D point where the total weight of the body may be considered to be concentrated.

• The average location of an object.• If an object rotates when thrown it rotates

about its center of gravity.• An object can be balance on a sharp point

placed directly beneath its center of gravity

Centroid• A 3D point defining the

geometric center of a solid.• Do not confuse centroid with the center of

gravity.– The two only exist at the same 3D point when

the part has uniform geometry and density.

Principal Axes

• The lines of intersection created from three mutually perpendicular planes, with the three planes’ point of intersection at the centroid of the part.

The X, Y, and Z axes show the principal axes of the ellipsoid.

Brodinski, K. G. (1989). Engineering materials properties and selection. Prentice Hall, Inc.: Englewood Cliffs, NJ.

Budinski, K. G. (1992). Engineering materials (4th Ed.). Prentice Hall, Inc.: Englewood Cliffs, NJ.

Gere, J. M., & Timoshenko, S. P. (1997). Mechanics of materials. PWS Publishing Company: Boston.

Lockhart, S. D., & Johnson, C. M. (1999). Engineering design communication: Conveying design through graphics (Preliminary Ed.). Addison Wesley Longman, Inc.: Reading, MA.

Madsen, D. A., Shumaker, T. M., Turpin, J. L., & Stark, C. (1994). Engineering design and drawing (2nd Ed.). Delmar Publishers Inc.: Albany.

Sources