Isaac Newton. What do we know about him, except that he was sitting under a tree and an apple fell on him, prompting him to think about the law of gravity? Almost nothing. But this great English scientist made a huge contribution to optics - the science of light and its nature, mathematics and astronomy. But today we are interested in his contribution to classical mechanics. For what merits did he recognize as the ancestor of classical mechanics and how many laws does Newton have? The article will answer these questions.
How many laws do Newton have and what are they about
Around us every day there are a lot of amazing and incredible things that do not seem to us as such only thanks to the school curriculum and the knowledge we gained. A few thousand years ago, people asked questions, many of which found rational answers. Isaac Newton made a huge breakthrough in the field of classical mechanics, thanks to which he went down in history.
Classical mechanics is the science of the movement of material bodies and the interaction between them. How many Newton's laws have formed the core of classical mechanics? Only three - fundamental and postulating this entire field of physics. They were not just born in the head of a great scientist. This is a collection of knowledge accumulated by millennial observations, classified by Galileo and formulated by Newton.
First law
We begin the consideration of the definitions of Newton's laws, naturally, from the first. It was deduced from the definitions of Galileo and sounds like this:
There are such reference frames called inertial, with respect to which material points, when no forces act on them (or mutually balanced forces act), are at rest or in uniform rectilinear motion.
It would seem that the law is more than obvious. But its formulation played a key role in the formation of mechanics as a science. Inertia is the ability of the body in some systems to maintain speed and trajectory constant. The apple lying on the table will not move unless you push it with your palm, and the car will not go for the same reason. Everything is simple.
However, this Newton’s law is not fully applied. Basically, it determines the movement of celestial bodies in space: there are no extraneous forces.
If a person untwists a core above his head and releases it, then under the influence of centrifugal force it will fly out of his hands and fly first along a straight path, and then change it under the influence of gravity and fall to the ground. If we imagine this situation in outer space, then the hammer, flying out of the “orbit” along which it was unwound, will fly strictly perpendicularly from it in a straight line, without changing its direction.
Newton’s first law has a trivial but very important scientific meaning. He says that any changes in the state of the body in space indicate that external forces act on it.
Second law
The first law showed us whether any forces affect the body under study, and the second law explains what happens to the body under the influence of these forces. The formula of Newton's law is presented in the figure below (F - force, a - acceleration, m - mass).
What does this law tell us? The stronger the forces affect the body, the greater the acceleration, and the greater the mass of the body, the acceleration is proportionally less. We apply this law only for inertial reference systems.
This Newton equation is one of the most popular and often used in classical mechanics. Indeed, thanks to him, knowing the magnitude, the direction of forces in the mechanical system and the mass of the body under consideration, we can calculate its position in space.
Third law
The third law is one of the most famous, which brought Newton popularity not only among physicists, but also among ordinary inhabitants. The third law, called Newton's law of gravity, is as follows:
Material points interact with each other by forces of the same nature, directed along a straight line connecting these points, equal in magnitude and opposite in direction.
Let's look at a standard Newtonian situation in which a plum, breaking away from a branch, falls to the ground due to the fact that the Earth acts on it by gravitational pull. But also, according to the third law of Newton, the plum acts on the Earth with the corresponding force. However, the mass of plums for a giant planet is so negligible that the force with which the plum influences the Earth can be neglected. We ourselves can feel that the force of the Earth acts on us, pressing on our soles, but we also act on the Earth with a proportional force, but it is as insignificant as plum.
The sun affects the planets of the solar system, but they do not fall on it, because in turn they affect it with equivalent force. Therefore, thanks to the third law, we can calculate the force with which two celestial bodies can influence each other according to the formula below:
where m 1 , m 2 are, respectively, the masses of the bodies under consideration, d 2 is the distance from the centers of both bodies, G is the gravitational constant.
The meaning of Newton's three laws in physics
So we figured out how many laws Newton has and what they mean. They were first published in 1687 and are still in use around the world. I. Newton combined, summarized all the previously obtained observations and laid the foundation for classical physics. And today, according to these laws, the movements of celestial bodies are considered and spaceships are designed. These laws made it possible to create a kind of mechanical system, a picture of the world that completely obeyed them.