Particle speed over lifetime Unity 3.5 particle system

Heya, I am trying to create a particle effect where all particles appears at the same time in the middle of a circle, and then plasts out from it. Then over time the speed of the particles should decrease.

But i cannot figure out where to change the speed over lifetime. The "velocity over lifetime" wants a specific direction, but I want all my particles to be in different directions, just the speed i want to change.

Anyone help?