A quantity is a number of units or a portion of a magnitude.
From the Latin quantitas , the 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 , because then I have to go back to the office" , "I think that in this World Cup, we are going to have a good number of scares in each match" , "That amount is more than enough to satisfy anyone" .
Quantities are expressed in different ways depending on the magnitude in question. A weight quantity can be expressed in grams ( “I'm not going to carry a lot of textured soy: two hundred grams is enough” ), while a length quantity can be expressed in kilometers ( “You still have a good number of kilometers to go before you reach the reservoir” ).
Quantities can be homogeneous (when they are made up of 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 precisely to avoid inconveniences. If a person wants to buy a car, he will need a certain amount of money. If he does not have this amount, he will not be able to complete the transaction.
In other situations, however, the quantities may be estimated or subjective (such as the amount of salt in a recipe or the number of changes of clothes to take on a trip). These are situations in which the taste of each person 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.
Popular sayings using this term include «quantity does not make quality » , with its variations, specific to each Spanish-speaking region. It is usually used in the sentimental plane (referring, for example, to the number of friends) as well as in the material plane ( «a quad-core processor does not necessarily offer better results than a two-core processor» ).
Weight quantities are usually expressed in grams.
The momentum
Momentum is a fundamental physical magnitude used in mechanical theories to describe the movement of bodies. In classical mechanics, its definition is obtained 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 to the work " Discourses and Mathematical Demonstrations Concerning 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:
* Newtonian mechanics defines it for a particle by multiplying its mass by its speed ;
* Hamiltonian or Lagrangian mechanics captures, 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.
Typically, Newtonian mechanics obtains the momentum and then seeks the relationship between it and Newton's laws ("Law of force", "Law of inertia", etc.). However, modern physics brought with it a number of new points of view, and the advantages of such procedures when working with momentum were questioned.
Mainly, it was shown 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 speed, which is why it ignores any non-massive body.