At Newton's laws explain countless everyday phenomena and are the basis of the study of mechanics, branch of physics which is dedicated to analyzing movements.
There are important observations about these laws which, if not carefully understood, can lead to errors in the interpretation of phenomena.
Below are five things you need to know about Newton's laws so that you don't make mistakes in interpreting and solving exercises.
1. mass and inertia
THE inertia, Newton's First Law, represents the difficulty imposed by an object to come to rest, if it is in motion, or to get in motion, if it is stationary. This law can be stated as follows: the tendency of an object at rest or in uniform rectilinear motion is to remain in its original state. The initial condition of the body can only be changed by applying an external force.
Another observation relates to pasta, which is the quantitative measure of inertia: the greater the mass of an object, the greater the difficulty imposed by it in putting itself at rest or in motion. The converse, in this case, is true, so the smaller the mass of an object, the less difficult it will be to change its initial condition.
2. Weight and normal
THE strength weight is a result of gravitational attraction existing between a planet and an object on its surface. This force is determined through the product of the object's mass and the value of the acceleration of gravity and will always be vertical and downwards, towards the center of the planet.
When an object is deposited on a surface, a vertical and upward force, called the normal force, arises on it. The surface applies this force to objects in order to support them.
Weight and normal are usually treated as a pair of action and reaction, but a careful analysis of Newton's Third Law shows that this is not true. THE law of action and reaction define that these forces, action and reaction, act in different bodies. When slapping a wall, for example, the action is made by the hand on the wall, while the reaction is made by the wall on the hand, therefore, there are two forces that act on two distinct bodies. As they act on the same body, weight and normal do not form a pair of action and reaction.
3. Limits of Newton's Laws
Newton's laws have two limits of application. If the velocities of the objects under analysis are close to or equal to the speed of light, Newton's laws must be replaced by relativistic proposals elaborated by Albert Einstein. Another application limit refers to the case where the dimensions of the objects involved are equal to those of subatomic particles. In this situation, these laws should be replaced by the laws of the Quantum Mechanics.
4. Validity of Newton's Laws
O referential it is the body from which observations about movement and rest are made. Newton's laws are valid only for frames that are at rest or in uniform rectilinear motion (so-called inertial references). In accelerated references, these laws lose their validity.
Imagine an airplane at the moment of acceleration for takeoff. Taking the aircraft, at that moment, as a reference, Newton's laws would not be valid, because, on takeoff, the plane has acceleration.
Attention! Our planet is considered an inertial reference, even if it performs movements with variations in speed.
5. Rewriting Newton's Second Law
Generally, the fundamental principle of dynamics, or Newton's Second Law, is represented by indicating the force as a result of the product of the mass and the acceleration of the object, but originally, Isaac Newton wrote that the force is a result of the variation of the amount of movement of the object as a function of time.
From this definition of Newton, one can arrive at the best known form of the Second Law:
FR = ΔQ
t
THE amount of movement is the result of the product of the object's mass and its velocity, thus, we have:
FR = m.Δv
t
Such as acceleration is defined as the ratio between the variation in speed and the variation in time, therefore, it is possible to represent the Second Law as follows:
FR = m.a
By Joab Silas
Graduated in Physics
Source: Brazil School - https://brasilescola.uol.com.br/fisica/cinco-coisas-que-voce-precisa-saber-sobre-as-leis-newton.htm
