Mass
From The DarkMod Wiki
Description
The mass spawnarg sets the mass of an entity. This is only useful for moveables, e.g. not necessary for static entities.
The mass must be in kilogramm and should be roughly the real mass of such an item. Realistic masses are the foundation of believable physics in game.
Examples
For instance, a carrot would have
"mass" "0.1"
to denote it weights 100 gr.