Foolish question:
When I use mass properties, does the "mass" listed list mass (lbm), or weight (lbf)?
If mass, do I still need to multiply by a gravitational constant to get a part's weight?
Thanks
Foolish question:
When I use mass properties, does the "mass" listed list mass (lbm), or weight (lbf)?
If mass, do I still need to multiply by a gravitational constant to get a part's weight?
Thanks
That's a really interesting question. Having looked at the Wiki on the difference between pound mass and pound force, I predict that SolidWorks is based on the latter. My guess is that SolidWorks doesn't account for attenuation of gravitational force with distance, especially with the model being limited to a bounding cube 1000m on a side.
It lists lbm. You do not have to multiply by g to get weight. Multiplying lbm times g would give units of weight, but not in pounds.
You'd only multiply by g to get weight in the English system if the mass were given in slugs. The whole point of the lbm unit is that the multiplication is done for you. But this takes a lot of getting used to, and frankly, the lbm is a sorry and confusing unit. You can take it's definition to be: "Enough slugs to make 1 lbf in standard gravity".
As a check, assume the mass is given in lbf. Then multiplying by g would give units of force squared, which would not make sense.
As another check, take the mass from SolidWorks in lb and kg. Then convert the mass in lbm to kg in Google. You'll see the answers are the same.
The moral of the story is, always carry your units through your calculations. And be glad you don't have to do fluid calcs in the English system <shivers>
Mike was right.
Why not perform an experiment and find out? Draw a cube of know size. Assign a material whose density you know. See what mass properties says.
Jim S.