Momentum of a System question

[RevX]

Homework Statement

What has to be true in order for the momentum of a system to be conserved?

Homework Equations

The Attempt at a Solution

I am thinking the net force needs to be zero.

Just wanting to confirm this is correct.

Thanks in advance

 

[jfizzix]

In order for the total momentum of a system to be conserved, the net force on that system must be zero. In order for the total angular momentum to be conserved, the net torque must be zero.