Even though the magnitutes of action force are equl and their direction are opposite there effects do not get cancelled
Answers
Because they’re acting on different objects.
You’re thinking of Newton’s third law, right? Every action has an equal and opposite reaction?
I’m sitting on a chair, exerting my weight of X pounds on it, downward. That’s the action. The equal and opposite reaction is the chair supporting me with a force of X pounds upward.
When you fire a rifle, the rifle exerts a force on the bullet pushing it forward. That’s the action. The bullet exerts an equal force on the rifle, backward, bruising your shoulder if you’re not holding the rifle properly. I oversimplify; there’s an expanding charge in between, but the analysis is still valid.
That’s what Newton meant. More generally: if A exerts force F on B, then B exerts force F on A in the opposite direction.