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 is specified in kilograms and should be roughly the real mass of such an item. Realistic masses are the foundation of believable physics in game.
Note: you cannot enter zero mass values, the code will not accept this. The reason is that the inverse of the mass is needed for physics calculations, and zero masses would result in divisions by zero.
Examples
For instance, a carrot would have
"mass" "0.1"
to denote it weighs 100 gr.