"There is a difference between strength and force, especially in a scientific/physics context. They aren't interchangeable in science. "Force", in physics, is an influence that changes an object's velocity or shape. F=MA (Force = mass x acceleration). There is an electromagnetic force between two electrons. "Strength" in physics is the quantity of a force: its magnitude. You can have a strong force (a lot of strength) or a weak force (very little strength​). A force of 10 Newtons [unit of force] has more strength than a force of 5 Newtons. Therefore, what Newton's third law says is, for every force there is another force that is exactly its opposite: the same magnitude (strength) and in the exact opposite direction. If force 1 has a strength of 3 Newtons and goes to the left, its reaction force will have a strength of 3 Newtons and go to the right: <--- force 1 ---> reaction force In a normal, non-scientific context though, "force" and "strength" are more similar: "Force" can be a verb (to use a lot of effort to do something: he forced open the door), a noun (something powerful that alters something else: he was a positive force in the community; use the force, Luke!), or refer to the military (the air force; the armed forces). "Strength" is a noun only. (Its adjective form is strong.) It can mean the quantity of any of the forces mentioned above (the strength of the armed forces = the number of personnel), someone's capacity to do something, especially physical or muscular (he didn't have the strength to walk farther; I lift weights to increase my strength), or someone's inner will or determination (he called upon his inner strength to keep smiling; God, give me the strength to stay awake in Church!). I hope that helped more than confused! "

Similar but not the same, as above Example He used his strength to force open the closed door