i thaught that might be the case. but it doesn't matter that much. if i can adjust the density than i don't have to worry about much more. i was planning on using it only for concepts anyway. thanks again for all the help. this is about the best physics simulator i've used in a long time. it beats the Pro/Engineer mechanics simulator by a bit also .

well theres the problem . i had sketchy physics 3 RC1 instead of 3x. it works fine now. thanks for the help.

--edit--

another less important question: if i make a hollow sphere(i found out how to do it) is the mass really smaller or does it take into account only the outer sphere when i tell it to set the physics model to a sphere?

I would like to use sketchy physics to simulate a specific engineering problem that i am having in the real world. the problem has to doa a lot with a large number of 2.875 inch diameter wiffle balls. i was hoping to simulate this in sketchy physics, however i don't seem to be able to simulate the weight of them. i would like to simulate hollow balls not solid ones. so i would like to either change the density of the wiffle balls only, or else somehow hollow them out. i've tried so many methods but i can't seem to be able to do either things.

so how do i do this? is it possible to make a hollow ball in sketchup? or is it possible to change the mass or density of one object in sketchyphysics?