If the impulse is zero, there is no changeinmomentum.
如果冲量为零，则动量不变。
2
This force on the gun will cause a changeinmomentum for the gun - that's recoil.
施予枪的力将导致枪的动量改变-这就是后座力。
3
So the individual stars will change their momentum all the time, because the individual particles in the individual stars will experience, of course, the internal forces.