I am ttying to create a shot where the ground gradually splits over time causing a giant crack down the middle. When ever I have attempted this I have not been able to make it gradual since I cannot control rigid bodies along a path. If there is a way to create a shot like this, could someone please help. Thanks
Try making a line grow, then convert that line into extruded geometry. From there, boolean subtract it from a cube.
Okay,. I will have a go, thanks 
What would be your method of animating the line, do I need an addon?