How rotation of the Part influences ApplyImpulse?

I am using ApplyImpulse to push a Part with size 1,1, 8.
I notice that the rotation of the part before the push influences a lot the direction in which the part flies.
Why is that?
The force is always applied at the center of the part.
There is no air resistance in Roblox and I did not see this behaviour mentioned in the docs for ApplyImpulse?

Thanks in advance