When I make a part and then go to mass properties it gives me a weight.  Oftentimes this weight (mass) that SW tells me fails the sanity check.  Then I will check and find that no material is defined.

Why does Solid Works spit out a weight when there is no material defined?  Is there a logical reason for it to use the density it does when there is no material defined?

Part of me wishes that SW would throw out a warning when no material was defined rather than throwing out a random/wrong weight.  On the other hand, when I measure the weight of a big assembly, I don't want to have to worry about defining a material for every little bolt, nut and washer.

What do you folks think about this?