I know that we can rotate a deformable object using internal forces only in spac
ID: 1383159 • Letter: I
Question
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?
Explanation / Answer
No. Momentum is conserved. Since momentum is mass times the velocity of the center of mass, if the momentum is zero, the center of mass can't move. Alternately, if the center of mass is already moving, it will keep moving indefinitely in a straight line when there are no external forces.
However, in curved spacetime the above may not hold.