# Space torque semi-independent of center of mass

I am making a 2d user build spaceship game that allows the user to place thrusters where they would like. I've read a bunch of posts in a lot of places including stack exchange on how determine the lateral force and torque force.

My problem so far with the information that I have is that it seems to me that they all are assuming that the axis of rotation for torque will always be at the center of mass. Obviously a well designed thruster placement will have the rigid body rotate about its center of mass but some damage can ruin that and to be frank I want the user to be able to make not well designed ships just because it's fun.

My main question really is what terminology am I missing that allows me to find out the relationship between the center of thrust and the center of mass so that I can find the true rotation axis for torque.

Here is an example of a craft that won't rotate about its center of mass:

• I posted this on a separate forum as well and you are the second person to tell me that. If that is the case then not only is my job much easier but it also blows my mind. I feel like if I grab a pencil on its end but leave it on the table then apply similar forces as the image then it doesn't rotate around its center of mass. Hardly scientific I know but because I can't seem to google the right words for this specific problem its what I have to go on. Commented Aug 12, 2021 at 19:53
• I'm no physicist, but I think the underlying truth of rotation is that it doesn't exist (in our world). Physical rotations are just many translations tied together in a specific way. Like the idea of a rigidbody is just a super simplified model of our physical reality. You can imagine how a softbody is a truer model of reality where there is no rotation, just translations of nodes which are specific joints which make the body maintain some sort of coherent shape. You aren't "rotating" your pencil, you're pushing up against its particles which are rigidly interconnected so it maintains shape. Commented Aug 12, 2021 at 20:05