Force, operational definition

Thermodynamics describes the behaviour of systems in terms of quantities and functions of state, but cannot express these quantities in terms of model concepts and assumptions on the structure of the system, inter-molecular forces, etc. This is also true of the activity coefficients thermodynamics defines these quantities and gives their dependence on the temperature, pressure and composition, but cannot interpret them from the point of view of intermolecular interactions. Every theoretical expression of the activity coefficients as a function of the composition of the solution is necessarily based on extrathermodynamic, mainly statistical concepts. This approach makes it possible to elaborate quantitatively the theory of individual activity coefficients. Their values are of paramount importance, for example, for operational definition of the pH and its potentiometric determination (Section 3.3.2), for potentiometric measurement with ion-selective electrodes (Section 6.3), in general for all the systems where liquid junctions appear (Section 2.5.3), etc. 

The operational approach to the definition of fundamental concepts in science has been emphasized by Mach, Poincare, and Einstein and has been expressed in a very clear form by Bridgman [2]. (Operational definitions had been used implicitly much earlier than the twentieth century. Boyle, for example, defined a chemical element in terms of the experiments by which it might be recognized, in order to avoid the futile discussions of his predecessors, who identified elements with qualities or properties.) In this approach, a concept is defined in terms of a set of experimental or mental operations used to measure or to recognize the quantity The concept is synonymous with the corresponding set of operations (Bridgman). An operational definition frequently may fail to satisfy us that we know what the concept really is. The question of scientific reality has been explored by many scientists and philosophers and is one that every student should examine. However, in the operational approach, we are not concerned with whether our definition has told us what the concept really is what we need to know is how to measure it. The operational approach has been stated succinctly by Poincare in the course of a discussion of the concept of force ... 

Ideal liquids are incompressible and their flow is by definition frictionless. Real liquids are characterized by cohesion forces operating between the molecules, which bring about frictional forces, whose action is known as internal friction. 

On atomic volume On the laws regulating the combination betwixt atoms On the forces operating on living matter On the applications of the atomic theory, and on its relation to other physical laws Speculative inquiry into the elements of matter On the knowledge of the ancients with respect the law of definite proportions etc. 

L. C. Towle (Naval Research Laboratory) As I understand your comments today and your preprint you state that the friction force observed with polymers is not given by the expression F = pN. My understanding of the definition of the coefficient of friction is that it has an operational definition, i.e. to measure the friction between solids A and B one forces A to slide against B under measured load N and simultaneously measures the tangential force F. The friction coefficient is then defined to be the ratio p = F/N. If this is the case, then it would seem that one always has F = pN being valid. If this is not the case, then I wonder how does one define the friction coefficient ... 

A few comments on the layout of the book. Definitions or common phrases are marked in italic, these can be found in the index. Underline is used for emphasizing important points. Operators, vectors and matrices are denoted in bold, scalars in normal text. Although I have tried to keep the notation as consistent as possible, different branches in computational chemistry often use different symbols for the same quantity. In order to comply with common usage, I have elected sometimes to switch notation between chapters. The second derivative of the energy, for example, is called the force constant k in force field theory, the corresponding matrix is denoted F when discussing vibrations, and called the Hessian H for optimization purposes. 

The range of satisfactory operation for a gas burner, defined by light-back, blow-off and incomplete combustion is limited. The variation in gas analyses, particularly higher hydrocarbons and inerts, can influence the range of operation. This has led to the definition of different groups of natural gas. A practical effect is that burners designed for the European continent may not be suitable for the UK without adjustment. This does not apply to forced-draft burners. 

We see that we can attach a definite physical meaning both to the existence of a neutral molecule in solution, and to the dissociation of this molecule into a pair of ions. Consider points near P and near Q in Fig. 27c. A point on the curve near P corresponds to the situation where the distance between the nuclei of the two ions has, say, the value OA, while a point on the curve near Q corresponds to the separation OB. If the separation of the nuclei is increased from OA to OB, a considerable amount of work is done against the short-range forces of attraction, in order to go from P to Q. But at Q the short-range forces are no longer operative and the neutral molecule has been dissociated into a pair of ions, between which there is the usual electrostatic attraction. 

Starting with this definition the semiconductor diemical sensors can be arbitrary classified with respect to following features the type of electrophysical characteristics diosen for monitoring, such as electric conductivity, thermal-electromotive force, work function of electron, etc. type and nature of semiconductor adsorbent used as an operational element of the sensor and, finally, the detection method used for monitoring the adsorption response of electrophysical characteristics of die sensor. 

---