Third Newton's Law of Mechanics  

 Newton's third law states that when two bodies interact, they always exert equal and opposite forces on each other. This law is commonly known as the law of action and reaction. For example, a book lying on a table produces a downward force equal to its weight on the table. The third law states that the table exerts equal and opposite force on the book. The opposite force occurs because the weight of the book causes an invisible deformation of the table, which pushes the book upwards like a compressed spring. (Figure 2.)
According to the textbook's definition, every force has an equal and opposite reaction. If body A exerts a force on body B, body B will respond with an equal and opposite force.
When driving a nail with a hammer, for example, into wood, the nail will stop the hammer at the end of its swing. It is completely counterintuitive to believe that the force of the hammer and the counterforce of the nail are equal throughout the contact, not just at the end when the motion stops, which is before the hammer stops. As the hammer advances, the nail "gives" and drives into the wood, despite the fact that the forces between them remain equal throughout the motion, from initial contact to the end. (Figure 1.)

It should be noted that Newton's first law also describes the action of equal and opposite forces, but on the same object, and as a result of the balance of forces, the object rests or moves uniformly in a straight line. This is fundamentally different from Newton's third law, which deals with equal and opposite forces, where each force acts upon the other object. As a result, these forces can have varying effects on the objects. Much like the aforementioned nailing. Depending on the vector sum of all forces, the total force on each of these objects could be non-zero.
If the total force on the body is not zero, it changes velocity and moves according to Newton's second law. If the total force on a body is zero, either because there are no forces (which is impossible) or because all forces are perfectly balanced by opposing forces, the body is not accelerating and is said that forces are in equilibrium. Where rest is also a state of unchanged velocity, only that velocity is zero. Conversely, if a body is observed not to change velocity, neither in amount nor direction, we must conclude that the sum of all forces acting on that body is zero.

Convincing students of the ideas contained in Newton's third law — that there is an equal and opposite reaction to every force — can be difficult at times. If object A exerts a force on object B, object B responds with an equal and opposite force. As an auxiliary explanation, it is commonly stated that: if you push the wall with some force, the wall will push you back in the opposite direction with equal force. To overcome this difficulty, the following simple experiment can help. All of the students in the class should follow the instructions demonstrated with hands, and they repeat them for themselves. All you need for accessories is a wall and, of course, a hand to push it!