In that case, the object's rotational momentum won't change.
Yes. If an object is at rest or in a linear motion state at constant speed, the net force applied onto the object is zero.
When the net forces acting on an object sum to zero then the object's acceleration is zero.
If the net forces acting on an object amount to zero, that object is at rest.
Just as a net force is the vector sum of all the forces acting on an object, a net torque is the vector sum of all torques acting on an object.
-- four oxen harnessed at equal intervals to a millstone, grinding grain
Net torque is the magnitude and direction of torque that is left over when you add up the torques that are acting on an object.
There is none
If the net force on an object is zero then the object has zero acceleration, meaning that the speed and direction of its motion aren't changing.
The net force is zero.
Yes, the net force would be zero if all the forces acting on the object negated each other.
If all forces acting on the object are balanced (equal), the net force acting on the object is zero.
0. An object in equilibrium has constant velocity, which makes its acceleration 0. Since net force=mass times acceleration, this would make the net force zero. Note that there could be multiple forces acting on the object, but since it is in equilibrium they would have to be equal and opposite in direction, to cancel all of the forces out. This would make the net force zero.