This law shows that every action has an equal and opposite reaction. Specifically, if one object exerts a force on another object, it will also be subjected to the same but opposite force exerted by another object. This law also applies to the interaction between objects. For example, when we push an object, we will also be pushed by the same force.
Newton's third law reveals the essence of force, pointing out that force is the interaction between objects, and the force is equal in magnitude and opposite in direction, and acts on the same straight line. This law is isomorphic with Newton's first and second laws, which constitutes the foundation of classical mechanics and has a far-reaching impact on the development of physics.
In classical mechanics, the condition for the establishment of the third law is that macroscopic objects move at low speed. When the speed of an object approaches the speed of light, the magnitude of the acting force and the reaction force are generally no longer equal. For contact forces, the law is strictly established. For non-contact forces, such as gravity and electromagnetic force, the delay effect needs to be considered because of the interaction and propagation through the field at limited speed.
As far as gravity is concerned, the law still holds (strictly speaking, it should be "approximate") because in general mechanical problems, objects are close to each other and the relative motion speed is not large, and the gravitational field is considered to be stable. As for the electromagnetic force, besides the delay effect, another factor should be considered.
The characteristics of Newton's third law:
Newton's third law of motion studies the interaction mechanism between objects. The object of study is at least two objects, and the interaction between two or more objects can always be divided into several pairs of interacting objects.
Action and reaction are mutual, interdependent and interdependent, and both take the existence of the other party as the premise of their own existence. Without reaction, action does not exist; Force has materiality, and it cannot exist without objects (matter); Force is always produced by the interaction of two or more objects.
Newton's third law is also instantaneous, that is, the simultaneity of action and reaction, which are produced, disappeared and changed at the same time. Action and reaction are equal, so it doesn't matter who they are.