The force and reaction between two objects are always equal in magnitude and opposite in direction. A force cannot exist alone from an object. This is famous Newton's Third Law 。 （1） Force And reaction force have no priority or priority. It is generated and disappeared at the same time. (2) This pair of forces acting on different objects cannot be offset.
(3) The action and reaction must be forces of the same nature.
(4) The establishment of Newton's third law and Frame of reference Not relevant, in Non inertial frame in Newton's Third Law It is still established. (5) Pay attention to the difference between acting force and reaction force Counterbalance force 。 Why can a backward jet push the rocket forward? Why does the shell move backward when it moves forward? This is the principle of force and reaction. When object A exerts a force on object B, object B must reciprocate to object A at the same time; The acting force and reaction force are equal in magnitude, opposite in direction and acting on the same straight line. This is the commonness of all things in nature. When we walk, our feet push the ground backward (force), and the ground pushes our feet forward (reaction force) to make our bodies move forward. When rowing, the oars push the water backward (force), and the water pushes the oars forward Backstepping (reaction force) so that the ship can move forward. Similarly, the gas ejected backward pushes the rocket forward. Gun in At launch Apply a force on the shell. While the shell moves forward, the reaction force will make the shell move backward Humans have long discovered the relationship between force and reaction. For example, China Pre Qin Epochal Mozi The school once said, "The boatman hooks the stake on the bank with a bamboo pole, and the stake can pull the boat to the shore in turn." Later, the great scientist Newton The principle of force and reaction is summarized as Newton's third law of motion 。 
