mass: could affect how external forces accelerate the part. a part with a higher mass requires more force to be moved
collision weight: could affect how the part applies forces to objects it collides with. a lower collision weight means the part does not apply as much force to other parts
mass = density * volume. If you change the Density PhysicalProperty, you effectively change the mass.
Iām not sure collision weight makes much sense from a purely physical perspective. You should be able to achieve a similar effect by changing both Density and Elasticity.
i had no idea this was the case!! thanks for letting me know
i thought it might be useful in some niche cases, i think i meant that second suggestion more as a hypothetical than an actual feature