how to make particles stop, then regain velocity

hello, so i am kinda new to blender. like the title says, i want particles to stop, then regain velocity without their direction being changed. these particles will have 0 gravitational force and will emitted from 1 face. the effect i want is that all the particles stop as more particles are created, once all particles are created, they all regain velocity at the same time. i hope this is possible, thanks