A quantity is a number of units or a portion of a magnitude.
From the Latin quantitas , quantity is the portion of a magnitude or a certain number of units . For example: “We need a larger amount of money to move,” “Please don't serve me so much food , then I have to go back to the office,” “I think that in this World Cup, we are going to spend a good amount of time.” scares in every game” , “That amount is more than enough to satisfy anyone” .
Quantities are expressed in different ways depending on the magnitude in question. A quantity of weight can be expressed in grams ( "I'm not going to carry a lot of textured soy: two hundred grams is enough for me" ), while a quantity of length can be expressed in kilometers ( "You still have a good number of kilometers to go." before reaching the reservoir.”
Quantities can be homogeneous (when they are formed by objects of the same species), heterogeneous (composed of different species or substances), continuous (their parts cannot be separated) or discrete (their components are dispersed).
Exact or estimated amount
In some cases, the amount in question must be handled exactly to avoid inconvenience. If a person wants to buy a car, they will need a certain amount of money. If you do not meet this amount, you will not be able to complete the operation.
In other situations, however, the quantities can be estimates or subjective (such as the amount of salt in a recipe or the number of clothes to take on a trip). These are situations in which each person's taste comes into play, as well as a series of cultural issues, and any possibility is valid as long as it is accepted by the person considering it.
Among the popular sayings that use this term is "quantity does not make quality / " , with its variations, typical of each Spanish-speaking region. It is usually used on a sentimental level (referring, for example, to the number of friends) as well as on a material level ( "a quad-core processor does not necessarily offer better results than a two-core processor" ).
Weight quantities are usually expressed in grams.
The momentum
Known as quantity of motion , momentum, impetus or linear moment, a fundamental physical quantity used in mechanical theories to describe the movement of bodies. For classical mechanics, its definition is achieved by multiplying the mass of a body by its speed at a given point in time.
Its origins date back to the 17th century, more precisely from the work " Discourses and mathematical demonstrations around two new sciences ", published in 1638 by Galileo Galilei, in whose pages he refers to the concept through the term "impetus".
Ways to understand momentum
Depending on the mechanical formulation taken into account, the specific definition of momentum is different:
* Newton's mechanics defines it for a particle by multiplying its mass by its speed ;
* Hamiltonian or Lagrangian mechanics capture, in non-Cartesian coordinate systems, forms of greater complexity;
* the theory of relativity contemplates a definition of greater complexity even if inertial systems are used;
* Quantum mechanics requires for its definition the use of self-adjoint operators that are defined on an infinite vector space.
Generally, Newtonian mechanics obtains the momentum and then looks for the relationship between it and Newton's laws ("Law of force", "Law of inertia", etc.). However, modern physics brought with it a series of new points of view, and the advantages of such procedures when working with momentum were questioned.
Mainly, it was evident that this fundamental magnitude is a property belonging to every physical entity, whether or not it has mass (as can be seen in the case of photons and fields). The Newtonian formula is based on the product of mass and velocity, which is why it ignores any non-mass body.