- What are Newton's laws?
- Newton's First Law or Law of Inertia
- Second law or fundamental Law of dynamics
- Third law or Principle of action and reaction
- Isaac Newton Biography

We explain what Newton's Laws are, how they explain inertia, dynamics and the action-reaction principle.

Newton's laws allow us to understand motion.## What are Newton's laws?

Newton's Laws or Newton's Laws of Motion are the three fundamental principles on which classical mechanics is based, one of the branches of the physical. They were postulated by Sir Isaac Newton in his work *Philosohiae naturalis principia mathematica *("Mathematical principles of natural philosophy") of 1687.

This set of physical laws revolutionized the basic concepts regarding the movement of the bodies that humanity had. Together with the contributions of Galileo Galilei, it constitutes the basis of thedynamic. When combined with theUniversal gravitation law by Albert Einstein, allows us to deduce and explain Kepler's Laws on planetary motion.

However, Newton's Laws are valid only within inertial reference frames, that is, those that are not accelerated and in which only real forces intervene. Furthermore, these laws are valid for objects moving at a speed much slower than the speed of light (300,000 km / s).

Newton's Laws start from the consideration of motion as the displacement from one object from one place to another, taking into account the place where it occurs, which can also move at a constant speed in relation to another place.

## Newton's First Law or Law of Inertia

The Newton's first law contradicts a principle formulated in the antiquity by the Greek sage Aristotle, for whom a body could only retain its movement if a force sustained. Newton states instead that:

"Every body perseveres in its state of rest or of uniform rectilinear motion unless it is forced to change its state by forces impressed on it."

Therefore, an object that is moving or that is at rest cannot alter that state, unless some type of force is applied to it.

According to this principle, motion involves magnitudes that are vector (endowed with direction and sense). Acceleration can be calculated from initial and final velocity. In addition, he proposes that bodies in motion always tend to displacement in a straight and uniform path.

A perfect example of the law ofinertia he is constituted by a weight thrower in the Olympics. The athlete gains momentum by moving in circles, rotating the weight tied with a rope on its own axis (circular motion), until it reaches theacceleration necessary to release it and watch it fly in a straight line (uniform rectilinear motion).

This rectilinear motion continues until thegravity its trajectory is curving. At the same time, the object's friction with air slows down (negative acceleration) until it falls.

## Second law or fundamental Law of dynamics

Newton's second law relates force, mass, and acceleration.

In this law Newton defines the concept of force (represented by *F*), stating that:

"The change of a movement is directly proportional to the force printed on it and takes place according to the straight line along which that force is printed."

This means that the acceleration of a moving object always responds to the amount of force applied to it at a given moment, to modify its trajectory or speed.

From these considerations arises the fundamental equation of the dynamic for objects of constant mass:

Resulting force (Fresultant) = mass (m) x acceleration (a)

A net force acts on a body of mass constant and gives you a certain acceleration. In cases where the mass is not constant, the formula will focus more on the momentum (p), according to the following formula:

Amount of motion (p) = mass (m) x velocity (v). Hence: Fneta = d (m.v) / dt.

Thus, force can be related to acceleration and mass, regardless of whether the latter is variable or not.

To exemplify this second law, the case of free fall is ideal: if we drop a tennis ball from a building, the acceleration it experiences will increase as the weather elapses, since the force of gravity. Thus, its initial velocity will be zero, but a constant force will be applied to it in a straight line, downward.

## Third law or Principle of action and reaction

According to Newton's third law,

"Every action corresponds to an equal reaction but in the opposite direction: which means that the mutual actions of two bodies are always equal and directed in the opposite direction."

In this way, whenever a force is exerted on an object, it exerts a similar force on address opposite and of equal intensity, so if two objects (1 and 2) interact, the force exerted by one on the other will be equal in magnitude to that exerted by the other on the first, but of opposite sign.

That is: F1-2 = F2-1. The first force will be known as "action" and the second force as "reaction."

To demonstrate this third law, it is enough to observe what happens when two people of similar weight run in opposite directions and collide: both will receive the force of the other and will be thrown in the opposite direction. The same happens when a ball bounces off the wall and is thrown in address contrary, with a force similar to that which we project when we throw it.

## Isaac Newton Biography

Among other contributions, Isaac Newton discovered the color spectrum of light.Isaac Newton (1642-1727) was born in Lincolnshire, England. The son of Puritan peasants, his birth was traumatic and he came into the world so skinny and puny that they assumed he would not live long.

However, he grew up to be an eccentric child, with early talents for math and the philosophy natural. At the age of eighteen he entered the University of Cambridge to continue his studies. It is said that he entered the classroom very little, since his main interest was in the library and self-taught training.

This did not impede his academic development. He became a physicist, theologian, philosopher and mathematician of importance, recognized by the Royal Society. He is credited with the invention of mathematical calculus, as well as various studies on optics and light.

In addition, he contributed enormously to the development of mathematics and physics: he discovered the spectrum of color of light, formulated a law of thermal conduction, another on the origin of stars, about the speed of the sound at air and the mechanics of fluids, and a huge etcetera. His great work was the *Philosophiae naturalis principia mathematica*.

Newton died in 1727, having been a respected and honored scientist, receiving a lordly appointment ("sir") from Queen Anne of England. He suffered from renal colic and other kidney ailments which, after many hours of delirium, finally led him to his grave on March 31st.