Measure Bodies: Weight doesn't equal mass

[UserXX]

Hello Everyone,

I'm using NX5. I've assigned a material using TOOLS -> MATERIAL PROPERTIES. Using ANALYSIS -> MEASURE BODIES, the weight does not equal the mass.

In a previous post that appears to be from 2005, possibly using a different version of UG, under the PREFERENCES -> MODELING menu, you can make weight equal mass. I'm not seeing this option in NX5.

Who has a helpful suggestion to remedy this?

Thank you in advance...

 

[potrero]

One thought might be that if you have multiple solids in your part file, you might be actually counting different volumes in "Weight" vs measured mass...

perhaps, post a sample part?

 

[JohnRBaker]

I'm not aware of there ever being an option under...

Preferences -> Modeling...

...where I could have the system equate weight with mass, and I checked as far back as Unigraphics V16.0 (circa 1999). There is however an option to set the default Specific Density which is used when no Material has been assigned (the out-of-the-box default is set to the Specific Density of 'Steel') but that's about it.

Note that starting with NX 3, the Expression system started to apply dimensionality to Expression values including those derived from Mass Property calculations and it was at that point that we had to start differentiating between Weight and Mass since they use different units and represent different concepts, Mass being a property of the object itself, irrespective of your frame of reference, and weight being the FORCE which an object of a certain mass exerts based on the acceleration of gravity. Granted, when dealing with Earth-based objects at rest at sea level, one can generally assume that weight and mass can be used interchangeably, but with the Expression system there is still the issue of the units, since for Mass we use units Mass, such as kg and lbm (as well as Slugs), and for Weight, we use units of force, such as N (Newtons) and lbf. To accommodate that we provide a couple of special Functions to convert values from the conventional use of units in Metric versus Imperial units when equating Mass with Weight (these can be found under the 'f(x)' section of the Expression dialog under the Category 'Units'.

John R. Baker, P.E.
Product 'Evangelist'
Product Design Solutions
Siemens PLM Software Inc.
Cypress, CA

http://www.siemens.com/plm

http://www.plmworld.org/museum/

To an Engineer, the glass is twice as big as it needs to be.

 

[hudson888]

UserXX,

Could you tell us where you're taking the weight value from that you compare with the mass figure for measure bodies?

Are you just working with a component or could it be that you have an assembly with sub assemblies. I know that in some versions trying to get the weight data into a parts list draws a frustrating blank for the sub assemblies.

Best Regards

Hudson

www.jamb.com.au

Nil Desperandum illegitimi non carborundum