In which situation are unbalanced forces acting on an object?

Two people stand on opposite sides of a large tire. Both people push the tire with equal force.
Two people stand on opposite sides of a large tire. Both people pull the tire with equal force.
Two people stand on the same side of a large tire. Both people pull the tire with equal force.
Two people stand on the same side of a large tire. One person pushes the tire and the other pulls the tire with equal force.

The situation where two people stand on the same side of a large tire and one person pushes while the other pulls with equal force is an example of unbalanced forces acting on an object.