Weight - one of the main physical quantities. Meets to us both at the solution of physical tasks, and in everyday life almost every day. Let's talk about it and its calculation is more detailed.
Instruction
1. ""On fingers"", weight is amount of substance. And initially several centuries ago it and was defined. Really, it is quite logical. But in modern science these concepts are understood as several other things, and weight are subdivided into gravitational and inert. The first appears in the law of universal gravitation, is that allows to determine to us body weight. The second appears in the second law of Newton. It characterizes a measure of inertness of bodies. Both of them are proportional among themselves and the coefficient of proportionality accepted unit, that is actually they are equal, and it is proved experimentally therefore bases for input of special units of measure, the for each of them, are not present.
2. Weight in the special theory of relativity is defined by the ratio given on the picture above where E - the total energy of a body. Weight in the general theory of relativity is defined by the ratio presented on the second picture where with - the speed of light, to g - a metric tensor, p - an impulse. Thus a certain weight is a relativistic invariant, it means that it to equally same size in any reference system. If we pass to a system counting, in which this body will be based that, ratios will become simpler and weight will be defined by the relation of energy of rest to a square of the speed of light.
3. You should not confuse weight with weight. Weight is force and it is only proportional to weight. For example, in weightlessness of weight is not present due to the lack of g coefficient, but weight does not disappear anywhere. In everyday life, using scales, we tell ""a body so many kilograms weigh"", thereby meaning weight in value of weight, besides, that weight is measured just in kilograms, and here the weight, being force - in Newtons. But at the household, not scientific level it is standard and quite admissible.