Creating an emitter that emits particles with a velocity

[johnnyrainbow]

I've noticed that it seems possible to add a gravityForce behaviour to a particle system, but I did not find anything regarding a velocity or acceleration behaviour.

My particular intended use case is I would like to create an emitter can emit particles at a specified vector3 velocity (eg shooting rays from a gun towards a target). If there is another way I can achieve this please let me know! Thank you :)