On the Correct Way of Choosing a Frame of Reference in Mechanics and Thermodynamics and on Some Consequences

In the introduction, a brief history of the body selection that would define the inertial frame of reference in mechanics (and electrodynamics) is given. At the same time, attention has been drawn to Einstein's opinion about the (unrealized) causal relationship which should exist between the frame of reference and the law that is formulated from it. Therefore, parts 2 to 5 gradually present and elaborate the idea that, instead of directly choosing a body of reference, the criterion which will give legitimacy to the selection result should be defined first. And the criterion is such that the reference body is ensured by causality just mentioned by Einstein. Such a criterion for the fields of mechanics and thermodynamics is defined here and called the "criterion of observer's non-involvement in the observed” by a reference body. In the conclusion, as the main result, significant changes in the formulations of mechanics and thermodynamics, which the application of the criterion leads to, are stated. In those improved formulations the contents related to the observer are separated from the contents related to laws of nature.