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Molecular simulations of soft matter systems have been performed in recent years using a variety of systematically coarse-grained models. With these models, structural or thermodynamic properties can be quite accurately represented while the prediction of dynamic properties remains difficult, especially for multi-component systems. In this work, we use constraint molecular dynamics simulations for calculating dissipative pair forces which are used together with conditional reversible work (CRW) conservative forces in dissipative particle dynamics (DPD) simulations. The combined CRWDPD approach aims to extend the representability of CRW models to dynamic properties and uses a bottom-up approach. Dissipative pair forces are derived from fluctuations of the direct atomistic forces between mapped groups. The conservative CRW potential is obtained from a similar series of constraint dynamics simulations and represents the reversible work performed to couple the direct atomistic interactions between the mapped atom groups. Neopentane, tetrachloromethane, cyclohexane, and n-hexane have been considered as model systems. These molecular liquids are simulated with atomistic molecular dynamics, coarse-grained molecular dynamics, and DPD. We find that the CRW-DPD models reproduce the liquid structure and diffusive dynamics of the liquid systems in reasonable agreement with the atomistic models when using single-site mapping schemes with beads containing five or six heavy atoms. For a two-site representation of n-hexane (3 carbons per bead), time scale separation can no longer be assumed and the DPD approach consequently fails to reproduce the atomistic dynamics. [ABSTRACT FROM AUTHOR]

The representability and transferability of effective pair potentials used in multiscale simulations of soft matter systems is ill understood. In this paper, we study liquid state systems composed of n-alkanes, the coarse-grained (CG) potential of which may be assumed pairwise additive and has been obtained using the conditional reversible work (CRW) method. The CRW method is a free-energy-based coarse-graining procedure, which, by means of performing the coarse graining at pair level, rigorously provides a pair potential that describes the interaction free energy between two mapped atom groups (beads) embedded in their respective chemical environments. The pairwise nature of the interactions combined with their dependence on the chemically bonded environment makes CRW potentials ideally suited in studies of chemical transferability. We report CRW potentials for hexane using a mapping scheme that merges two heavy atoms in one CG bead. It is shown that the model is chemically and thermodynamically transferable to alkanes of different chain lengths in the liquid phase at temperatures between the melting and the boiling point under atmospheric (1 atm) pressure conditions. It is further shown that CRW-CG potentials may be readily obtained from a single simulation of the liquid state using the free energy perturbation method, thereby providing a fast and versatile molecular coarse graining method for aliphatic molecules. [ABSTRACT FROM AUTHOR]

We continue our investigation of the properties of matter at nonequilibrium steady states using a thermodynamic formalism derived from molecular fluctuations. Based on the generalized Clausius inequality, we extend the definition of ‘‘reversible’’ process to include transformations between steady states and relate reversible work and heat to changes in state functions. The variable which is thermodynamically conjugate to the internal energy, that is, the inverse of the generalized thermodynamic temperature, is an integrating factor for the reversible heat. We discuss the relationship of the generalized temperature to the Kelvin temperature, how the generalized intensive variables can be measured, define generalized heat capacities, and obtain the Gibbs–Duhem relationship satisfied by the intensive variables. These ideas are illustrated for two simple steady state systems, a fluid under homogeneous shear and a two level gas which is pumped by radiation. Finally we analyze under appropriate conditions the electromotive force of a chemical reaction system held at a nonequilibrium state. We predict corrections to the Nernst equation which depend on how far the chemical reactions are removed from equilibrium. [ABSTRACT FROM AUTHOR]

The article discusses the concepts of work and inertia frames with the help of a used car.

Choosing a system of interest and identifying the interactions of the system with its environment are crucial steps in applying the relation between work and energy. Responses to problems that we administered in introductory calculus-based physics courses show that many students fail to recognize the implications of a particular choice of system. In some cases, students do not believe that particular groupings of objects can even be considered to be a system. Some errors are more prevalent in situations involving gravitational potential energy than elastic potential energy. The difficulties are manifested in both qualitative and quantitative reasoning. [ABSTRACT FROM AUTHOR]

Based on a geometric demonstration by Johann Bernoulli, we show that the principles underlying the work-energy theorem are more fundamental than those discussed in the standard derivations. By introducing the notion of a mechanical Bernoulli process—a systematic process for destroying velocity and measuring work—we derive the relationship between the amount of work and the square of the velocity solely from the superposition of motion and the law of inertia. [ABSTRACT FROM AUTHOR]

Discusses the relation of the concepts of work and energy in introductory physics. Correlation of center-of-mass work with mechanical energy; Information on the change of an energy of a system in particle work; Sample problems for categories involving a rolling spool and a deformable system.

Describes the multirepresentation method used for teaching work-energy concepts. Work-energy processes and bar charts; Qualitative representations of work-energy processes; Quantitative work-energy problem solving; Student evaluation using the method.

Discusses the development of energy concepts in the teaching of introductory physics. Conservation of energy calculations; Association of energy transformations with zero-work forces; Definition of work; Connection between mechanical and thermal energy changes; Concept of internal energy; First Law of Thermodynamics.

Discusses the use of a test data in measuring horsepower and torque curves of an automobile. Types of tests performed to determine the power and torque of the engines of automobiles; Overview of a performance test data of an automobile; Results of the analysis of the automobile performance test data.

Presents a calculus- and algebra-free derivation of the best angle to drag a box. Steps in finding the best angle; Analysis of a moving box.

Presents a set of physics challenges for teachers and students. Computation of the length of three boards with the same mass, size and shape; Calculation of the amount of work done on lifting a small bucket that rests at the bottom of a pit; Acceleration of blocks of equal mass connected by an ideal string.

Comments on the article 'Physical and Colloquial Meanings of the Term Work,' published in 2003 issue of the 'American Journal of Physics.' Mechanical transfer of energy; Force-displacement product.

Responds to the comment made on the article 'Physical and Colloquial Meanings of the Term Work,' published in 2003 issue of the 'American Journal of Physics.' Distinction between input and output when talking about work; Need for students to learn about physics terminologies.

Comments on the use of the term work in physics. Reasons for not using the term; Proposal on the use of the term force-displacement product or force-displacement integral to substitute for the term word; Advantages of the proposed terminology; Extension of the suggestion to other terminologies in physics.