More than three centuries ago, the man considered by some scholars to be the most intelligent person in history, wrote a document that forever revolutionized the history of science. Entitled ‘Philosophiæ naturalis principia mathematica’, it contains the cornerstone of classical mechanics, it stipulates Newton’s three Laws thanks to which we can understand the movement of bodies and their behavior.
Isaac Newton, together with Galileo Galilei, laid the mathematical foundations for what we know today as classical mechanics or classical physics. Newton stipulated a first approach to understand the unit of measurement with which we can quantify bodies and that he would call ‘mass’, which in this theoretical framework should be understood as the amount of matter of an object. A concept that changed the way in which the interactions of reality are understood, because thanks to it it is possible to understand the behavior of objects.
The next premise that Newton teaches us is that the momentum of objects intrinsically depends on the amount of matter they possess. Therefore the dose of movement they experience is the product of mass and speed. But he also introduces us to a concept that will change science forever, that of force. According to Newton, forces are closely related to movement, since they are the causes and also the results of it.
In accordance with these premises, there are main laws that dictate the interaction of bodies in our reality and that are the most important of all classical mechanics. There are three in total and they could be briefly described as follows: the law of inertia, the relationship between force and acceleration and perhaps the best known of all, the law of action and reaction.
What are Newton’s Laws?
Newton’s first law (law of inertia)
Newton analyzes a very everyday fact and transforms it with great genius into the first law of classical mechanics. Better known as the law of inertia, this tells us about the origin of movement, that is, how a body begins to experience movement.
Writing in Latin in his masterful ‘Philosophiæ naturalis principia mathematica’, Newton tells us that “every body continues in its state of rest or uniform motion in a straight line, not far from the forces impressed to change its position.”
This tells us that a body cannot change state on its own, but requires a force to change its state of rest or uniform rectilinear motion. Unless a force is imprinted on such an object, no change will happen on its own.
Although it may seem like a fairly obvious premise, its value lies behind the power of analysis that brings us closer to great assumptions. Thanks to this law, Newton was able to understand that if the Moon did not shoot in a straight line tangential to its orbit, it was because another force was acting on it. Thus he understood that this force that constantly diverted the path of the Moon until it became an everlasting orbit was gravity and thanks to Kepler’s third law, he managed to mathematically demonstrate that this force was the same one that made apples fall on Earth.
Newton’s second law (fundamental law of dynamics)
The order that can be perceived in Newton’s laws is of a scientific beauty that few are able to appreciate. That is, first he explains to us the origin of the interactions of bodies, a concept that we know as movement and now in his second law, he describes the nature of said action. With it he shows us the result of applying force to an object to cause its movement.
Newton tells us that “the change of motion is directly proportional to the impressed motive force and occurs along the straight line along which that force is impressed.”
From this second law emerges perhaps the most well-known and memorable formula of the English physicist, which describes that the acceleration that a body experiences is directly proportional to the force it receives, which mathematically translated would look like this: F=mxa
Newton’s third law (principle of action – reaction)
This law has stood out among all thanks to its composition that borders on the poetic and functions as a kind of reflection on life. However, in science its application is of utmost importance to describe the movement of bodies.
“With every action, an equal and opposite reaction always occurs: it means that the mutual actions of two bodies are always equal and directed in opposite directions.”
This last principle completes the puzzle of the Newtonian system and turns it into a complete logical set that helps us understand the interactions of objects and the behavior of their movements. These three laws have led scientists to discover great things, such as the forces exerted between the Earth and the Moon, and also, to put into formulas practically the behavior of everything around us. Although Newton’s Laws were written more than three centuries ago, they are still valid in classical mechanics, although not in quantum mechanics and other sciences.