Weight and mass are two concepts and distinct physical quantities, but even now, in everyday speech, the term "weight" is often used incorrectly as a synonym for mass, which is a scalar quantity. The Academy itself recognized this confusion in the definition of "Weighting": "Determining the weight, or more properly, the mass of something by the scale or equivalent facility."
In classical physics, the weight is a measure of the gravitational force acting on an object. The weight corresponds to the force exerted by one body on a support, caused by the action of the local gravitational field on the mass of the body. As a force, the weight is represented as a vector, defined by its magnitude and direction, applied in the center of gravity of the body and directed approximately towards the center of the Earth.
The Newtonian concepts of gravity were challenged by relativity in the 20th century. The Einstein equivalence principle all observers placed in the same plane. This led to an ambiguity as to what exactly is meant by the "gravity" and therefore weight. The ambiguities introduced by relativity led, starting in the 1960s, to considerable debate in the education community on how to define the weight of their students. The election was a Newtonian definition of weight as the force of an object at rest on the ground due to gravity or an operational definition defined by the act of weighing. In the operational definition, the weight becomes zero, as in weightlessness in Earth orbit or free fall in a vacuum. In such situations, the Newtonian is that there remains a force due to gravity is not measured (thus causing an apparent weight of zero) while the Einsteinian view is that there is never a measurable force due to gravity (including the ground), but, in free fall, no force can be measured because the soil does not exert mechanical force is ordinarily observed as "weight".
The mass, in physics, is a measure of the quantity of material which has a body. It is an intrinsic property of the body that determines the extent of the inertial mass and gravitational mass. The unit used to measure mass in the International System of Units is the kilogram (kg). It is a scalar quantity.