Unbalanced forces are present when the total force acting on an object is not zero, meaning the object will accelerate in the direction of the net force. In the given options, the situation that describes unbalanced forces is:
"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."
This situation creates a different net force on the tire compared to the situations where equal forces are applied in the same or opposite directions, which would create balanced forces.