What is Newtonian Physics?
Isaac Newton is one of the greatest scientists in all of history, possibly the physicist-mathematician who left the most valuable and influential legacy, the Newtonian Physics. Newton extended the earthly laws of mechanics to the entire cosmos, which implied that nature is governed by universal laws. In his Principia (1687) he enunciated the Law of Universal Gravitation and the laws of motion. In his work Opticks (1704) he studied the nature of light, formulated the principles of optics and the theory of color. He also developed the integral and differential mathematical calculus. In 1672 he presented to the Royal Society the first reflecting telescope of practical utility that would have enormous significance in the further development of Astronomy.
Newtonian Physics took as its starting point a universe made up of large corpuscles and space. Each of them with the property of acting at a distance, that is, of exerting forces directly and instantaneously on the others. With this basic scheme, Newton developed his well-known theories of motion and gravitation published in 1686.
Newtonian Mechanics describes how forces produce motion: The proportionality between the intensity of the force and the acceleration (second law). The law of inertia (first law) by which a body remains in its state of motion if no forces act on it. The principle of Action and Reaction (third law), by which the force exerted by a body on a second body is equal and opposite to that exerted by the second on the first.
First law or law of inertia
Newtonian Physics first law, also known as the law of inertia, says that, if no other acts on a body, it will remain indefinitely moving in a straight line with constant speed, even so, if it is at rest since it is equivalent to zero speed.
In nature there is no rest, all matter is in motion, so when we speak of rest or Uniform Rectilinear Motion (URM) the word "relative" must be added (relative to a reference system). The body is at rest or in URM only concerning that frame of reference. When a body is at relative rest on the surface of the Earth, it is participating in the different movements that the planet makes and is subjected to different forces such as the gravitational forces of the Earth, the Sun, the Moon, and other bodies, as well as the mechanical resistance that prevents it from sinking into the ground or sliding. It can be said that the body is in equilibrium on the surface of the Earth and therefore in relative rest.
The movement is relative, that is, it depends on which observer is describing the movement. Thus, for a passenger on a train, the controller comes walking slowly down the corridor of the train, while for someone watching the train pass from a station platform, the controller is moving at great speed. Therefore, a reference system is needed to refer to the movement which I mentioned earlier. Therefore, Newton's first law serves to define a special type of reference system known as inertial reference systems, which are those reference systems from which it is observed that a body on which no net force acts moves with constant speed.
Second law or fundamental principle of dynamics/motion
Newtonian Physics second law is a law that allows us to understand the causes of motion, both in the heavens and on the earth, on our planet and on others, which serves both to understand why an object falls to the ground and to understand why it falls. The moon revolves around the Earth. Newton's second law created a new concept, force, and that new concept allowed us to understand movements, which is why it is known as the Law of Motion.
When an object goes from rest to movement, its speed changes, that is, it accelerates. And it will be easier to move an object of greater mass than one of lower mass. That is, Force, equals mass times acceleration. The force is proportional to the acceleration that a body acquires when moving, and the mass will be the constant of proportionality.
Third law or principle of action-reaction
This law states that whenever a body exerts a force on a second body, the second body exerts a force on the first whose magnitude is equal, but in the opposite direction to the first. Each force that acts on a body, it performs a force of equal intensity and direction, but in the opposite direction on the body that produced it. In other words, the forces, located on the same line, always appear in pairs of equal magnitude and opposite in direction.
The third law, also known as the Principle of Action and Reaction, essentially tells us that, if a body A exerts an action on another body B, it carries out another equal and opposite action on A.