Hey, I don't really know if it is a bug or am I doing something wrong but it used to work in previous versions of Unity. I create empty scene, stick a particle system in there as main object in hierarchy. I'm selecting simulation space to World, setting rate over distance to 10, move the object and it doesn't spawn any particles. The only thing that's kind of new to me is the "emitter's velocity" but none of the options there change the output - I'm not emitting any particles. I've tried to add inherit velocity but no change also. I'm using unity 2017.3. I've tested this also in 2017.2 and same effect. In 5.6.2p1 it works well but there is no "emitter velocity" in Main Module. @richardkettlewell has something changed or is it a but?