I know that we can rotate a deformable object using internal forces only in space. Thus we can cause an angular displacement without the use of any external forces.
The following youtube video shows are real life example to do so - http://www.youtube.com/watch?v=RtWbpyjJqrU
My question is
Can we do the same with linear motion also? By that I mean, can we cause a displacement in an object using only internal forces. I could not think of such a setup. And if we can what makes the angular displacement more special than linear displacement?