Question

Do we need to apply force to change center of mass?

Answer 1

or is there any other way to change center of mass?

Answer 2

Add more mass to the object at a point that is not the geometric center of mass.

Answer 3

Just to add a point, no force can change the center of mass of a body, because mass is an-ever constant quantity in newtonian mechanics. An external force may displace the center of mass, and also the body. So, with respect to the body, the center of mass's position remains unchanged.
But I think that a force may change the center of gravity of an object.

Answer 4

I suppose you are asking that is force reqd to change position of CoM wrt to the body itself, right?

Suppose you have system of two particles, whose CoM lies at their geometrical centre. Now, to dislocate its CoM, you move away one particle from the other, keeping another's location constant . As the distance between the two parts increases, the CoM too moves away from the original location.

Now, guess what did you require to change the CoM's location? external force - to move one particle from its current state of rest or motion!! (remember newton's first law?)

So, now the same system has its CoM at a different point! thanks to one man, "force"!

and @mani_jha , one reminder, centre of mass and centre of 'gravity' are not exactly the same things. Do check it out mate:
http://en.wikipedia.org/wiki/Center_of_mass#Gravity

Answer 5

Right Apoorv, they're not. That's why the center of gravity can be changed when the center of mass cannot(Stable,Unstable equilibrium)

Answer 6

hmm.. good point..!! variable force field. yes...!!!

Answer 7

ya @Mani_Jha is correct

Answer 8

by applying a force u dont change the position of COM with respect to the body
but u do change the position of the COM with respect to a point outside the body(in other words in this case as u move the body, its COM moves along with it)