We explain what Newton’s laws are and what their theoretical foundations are. Also, its features and applications.
What are Newton’s Laws?
Newton’s laws or Newton’s laws of motion are known as the set of theoretical principles that explain most of the phenomena observed and studied by classical mechanicsa branch of physics that analyzes the motion and energy of bodies.
These laws are the cornerstone of modern physicsalong with Galileo’s transformations that, when compared with the Laws of universal gravitation, allow us to obtain and explain Kepler’s Laws that account for planetary motion.
These laws were published in 1687 in the work Philosophiae naturalis principia mathematica of Newton (“Mathematical principles of natural philosophy”), among other discoveries of mechanics and mathematical calculation, considered the most important scientific work in the history of physics.
See also: Laws of Thermodynamics
Who was Isaac Newton?
Isaac Newton was an English physicist, theologian, philosopher and mathematiciancredited with the invention of mathematical calculus and numerous studies on optics and light.
His contributions to mathematics and physics are numerous and recognized.such as the discovery of the color spectrum of light, the formulation of a law of thermal conduction, proposals on the origin of stars, studies of the speed of sound in air and fluid mechanics.
His great work, however, is the Philosophiae naturalis principia mathematica and, above all, the three laws of motion.
Historical background to its laws
The speculations of the Greek philosopher Aristotle regarding motion They were considered valid for many centuries, even despite suspicions of their inaccuracy.
Later scholars of the movement such as the Spanish Juan de Celaya and his disciple Domingo de Soto, continued the studies of uniformly accelerated motion and free fall, laying the foundations for what would later be the revolutionary studies of the Italian Galileo Galilei (who introduced the steps of the scientific method) and those of the British Isaac Newton. (who first formulated the complete principles of the movement).
Theoretical fundament
Newton’s elementary formulations started from the consideration of movement as the translation of an object from one place to anotherunderstanding it as a relative concept with respect to an origin that, in turn, may be in motion with respect to another reference point, that is, Newton understood the importance of distinguishing between relative and absolute motion.
Newton started from the concept of mass (m)which he considered as the quantity of matter present in a body. The amount of movement is understood as the mass multiplied by the velocity (v).
Newton’s First Law: Law of Inertia
Newton’s First Law It contradicts a principle formulated by Aristotle.which postulated that a body can only maintain its motion if a sustained force is applied to it. Newton’s law states 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 upon it.”
So, An object that moves or rests cannot alter its state without some type of force being applied to it.. The movement according to this principle is a vector dimension (which has direction and sense), and allows the calculation of acceleration (positive or negative) from the variation in speeds.
Inertial reference systems
This first law allows the definition of a special type of reference systems that are known as inertial reference systems. With them, one can distinguish between the apparent motion of an object, if the observer is moving with it, or if on the contrary he is at a fixed point with respect to the moving object:
- Inertial observers. They are those in whose perspective Newton’s laws are fulfilled because they observe the movement of the object from “outside” and from a static point. If they exist, they could appreciate the “true” movement.
- Non-inertial observers. They are those that are subjected to forces and, therefore, their perspective of movement is relative, since they are immersed in the set of forces in the plane of the object.
Newton’s Second Law: Fundamental Law of Dynamics
This law deals with defining the concept of force (F). In principle it states: “The change of a movement is directly proportional to the driving force impressed 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 responds to the amount of force applied to modify its displacement.
Thence the fundamental equation of dynamics is bornfor objects of constant mass: Resultant force (Fresultant) = mass (m) x acceleration (a). A net force acts on a body of constant mass and gives it a proportional acceleration.
In cases where the mass is not constant, This formula will vary, and will be written as a function of the momentum (p)calculable according to the formula: Momentum (p) = mass (m) x velocity (v). Therefore:
Fneta = d (mv) / dt. Thus, force can be related to acceleration and mass, regardless of whether the latter is variable.
Conservation of momentum
This principle, which follows from Newton’s Second Law, allows us to describe the physics of collisions between moving objects:
- Elastic collision. The momentum (p) and kinetic energy of the colliding objects are conserved.
- Inelastic collision. The momentum of the two-body system (p) is conserved but the kinetic energy of the objects in the collision is not. Both bodies can suffer deformations and increase in temperature, and can remain united with each other after the collision.
Newton’s third law: principle of action and reaction
This law states: “For every action there is an equal but opposite reaction, that is, the mutual actions of two bodies are always equal and directed in opposite directions.” This means that For every force exerted on an object, it exerts an equal force but in the opposite direction. about the first.
Thus, if two objects 1 and 2 interact, the force exerted by 1 on 2 will be equal in magnitude to that exerted by 2 on 1, but of opposite sign: F12 = F21. The first will be called “action” and the second “reaction”.
Proof of the third law
It is easy to demonstrate this third law from everyday experiments. For example, when two people of similar weight push each other Both receive the impulse but are thrown in the opposite direction. The same thing happens when we bounce a ball off a wall: it will be thrown in the opposite direction with the same force as the one we applied when throwing it.
Contributions after Newton
After Newton’s formulations, many subsequent scientists have studied the principles and simplified them for application to non-inertial systems, such as Jean d’Alembert in his Treatise on dynamics (1743) or Louis de Lagrange in the 19th century.
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