While rotating an object or while openning a door or a water tap we apply a force or forces. Under which conditions is this process easy for us? Why? Define the vector quantity concerned. How does it differ for a single force and for two opposite forces with different lines of action?

Choose the correct options Consider following pair of forces of equal magnitude and opposite directions: (p) Gravitational forces exerted on each other by two point masses separted by a distance. (Q) Couple of forces used to rotate a water tap. ( R ) Gravitional force and normal force experienced by an object kept on a table. For which of these pair//pairs the two forces do NOT cancel each others's translational effect?