Forces within Static Particle Animation

Hi blender-people,

i’ve got a small question.

I want to know how i can animate forces for Static particles over a timeline, havent found any controls over ipo.

I want to do a splash effect. At the beginning of the anim the hair should hang down affected by the z-axis force and over 100 frames for example it should mimimize z-force to 0 and substitute it by a normal initial speed.

In the end it shall look like pikes of an hedehog.

Would be nice to know how to control forces.

Thanks for your help.