The [documentation] 1 in Unity states:
“You should strive to keep mass close to 0.1 and never more than 10. Large masses make physics simulation unstable.”
Someone in this thread, used a value of 1500 for a car and seems to work out well. In regards of the docs as quoted above. Why? Why is so significant with “0.1”?
Large relative mass differences cause problems in some interactions, such as when a light object gets squashed between two heavy objects, or between a heavy object and the ground. The constraint solver ends up needing more iterations to get a good solution, so depending on the implementation it either uses more CPU or it settles for a worse solution in which the collisions are not well-resolved.
For simple cases it’s likely to work fine though and I doubt that the absolute value of the mass matters much, it’s probably only the ratios between interacting objects’ masses that matter. If you do use extreme values, just make sure you test interactions with other objects thoroughly.