Choose a heavy object like a table or a box, which you can move only by pushing hard. Try to push it all by yourself. Can you move it? Now ask one of your friends to help you in pushing it in the same direction fig (a). Is it easier to move it now? Can you explain why? Now push the same object, but ask your friend to push it from the opposite side Fig. (b). Does the object move? If it does, note the direction in which it moves. Can you guess which one of you is applying a larger force?
(i) The box moves with difficulty when we push alone but moves easily if helped by our friend. Thus, force applied on an object in the same direction add to one another.
(ii) When the object is pushed from the opposite side, it does not move. Thus, if two forces acting in the opposite direction on an object the net force acting on it is the difference between the two forces.