To understand newton's 3rd law, which states that a physical interaction always generates a pair of forces on the two interacting objects. in principia, newton wrote: to every action there is always opposed an equal reaction: or, the mutual actions of two bodies upon each other are always equal, and directed to contrary parts. (translation by cajori) the phrase after the colon (often omitted from textbooks) makes it clear that this is a statement about the nature of force. the central idea is that physical interactions (e. g., due to gravity, objects touching, or electric forces) cause forces to arise between pairs of objects. each pairwise interaction produces a pair of opposite forces, one acting on each object. whatever the physical cause of the interaction, the force acting on object a due to object b is equal in magnitude and opposite in direction to the force acting on object b due to object a. incidentally, newton states that the word "action" denotes both (a) the force due to an interaction and (b) the changes in momentum that it imparts to the two interacting objects. if you haven't learned about momentum, don't worry; for now this is just a statement about the origin of forces. mark each of the following statements as true or false. if a statement refers to "two objects" interacting via some force, you are not to assume that these two objects have the same mass. answer part correctly to receive all pointspart aevery force has one and only one 3rd law pair force. truefalsepart bthe two forces in each pair act in opposite directions. truefalsepart cthe two forces in each pair can act on the same object or on different objects. truefalsepart dthe two forces in each pair may have different physical origins (for instance, one of the forces could be due to gravity, and its pair force could be a normal contact force).truefalsepart ethe two forces of a 3rd law pair always act on different objects. truefalsepart fgiven that two objects interact via some force, the accelerations of these two objects have the same magnitude but opposite directions. (assume no other forces act on either object.)truefalsepart gaccording to newton's 3rd law, the force on the (smaller) moon due to the (larger) earth isgreater in magnitude than, and in the opposite direction from, the force on the earth due to the moon. greater in magnitude than, and in the same direction as, the force on the earth due to the moon. equal in magnitude to, and in the opposite direction from, the force on the earth due to the moon. equal in magnitude to, and in the same direction as, the force on the earth due to the moon. smaller in magnitude than, and in the opposite direction from, the force on the earth due to the moon. smaller in magnitude than, and in the same direction as, the force on the earth due to the moon.