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Entropy02:39

Entropy

34.9K
Salt particles that have dissolved in water never spontaneously come back together in solution to reform solid particles. Moreover, a gas that has expanded in a vacuum remains dispersed and never spontaneously reassembles. The unidirectional nature of these phenomena is the result of a thermodynamic state function called entropy (S). Entropy is the measure of the extent to which the energy is dispersed throughout a system, or in other words, it is proportional to the degree of disorder of a...
34.9K
Entropy01:18

Entropy

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The first law of thermodynamics is quantitatively formulated via an equation relating the internal energy of a system, the heat exchanged by it, and the work done on it. A quantitative formulation of the second law of thermodynamics leads to defining a state function, the entropy.
When an ideal gas expands isothermally, the disorder in the gas increases. From the molecular perspective, the gas molecules have more volume to move around in.
Consider an infinitesimal step in the expansion, which...
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Second Law of Thermodynamics02:49

Second Law of Thermodynamics

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In the quest to identify a property that may reliably predict the spontaneity of a process, a promising candidate has been identified: entropy. Processes that involve an increase in entropy of the system (ΔS > 0) are very often spontaneous; however, examples to the contrary are plentiful. By expanding consideration of entropy changes to include the surroundings, a significant conclusion regarding the relation between this property and spontaneity may be reached. In thermodynamic models, the...
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Second Law of Thermodynamics00:53

Second Law of Thermodynamics

67.7K
The Second Law of Thermodynamics states that entropy, or the amount of disorder in a system, increases each time energy is transferred or transformed. Each energy transfer results in a certain amount of energy that is lost—usually in the form of heat—that increases the disorder of the surroundings. This can also be demonstrated in a classic food web. Herbivores harvest chemical energy from plants and release heat and carbon dioxide into the environment. Carnivores harvest the...
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Entropy and the Second Law of Thermodynamics01:20

Entropy and the Second Law of Thermodynamics

4.8K
The second law of thermodynamics can be stated quantitatively using the concept of entropy. Entropy is the measure of disorder of the system.
The relation  between entropy and disorder can be illustrated with the example of the phase change of ice to water. In ice, the molecules are located at specific sites giving a solid state, whereas, in a liquid form, these molecules are much freer to move. The molecular arrangement has therefore become more randomized. Although the change in average...
4.8K
Third Law of Thermodynamics02:38

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21.6K
A pure, perfectly crystalline solid possessing no kinetic energy (that is, at a temperature of absolute zero, 0 K) may be described by a single microstate, as its purity, perfect crystallinity,and complete lack of motion means there is but one possible location for each identical atom or molecule comprising the crystal (W = 1). According to the Boltzmann equation, the entropy of this system is zero.
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An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids
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Negative Mass in the Systems Driven by Entropic Forces.

Edward Bormashenko1, Artem Gilevich1, Shraga Shoval2

  • 1Department of Chemical Engineering, Biotechnology and Materials, Faculty of Engineering, Ariel University, Ariel 407000, Israel.

Materials (Basel, Switzerland)
|September 13, 2025
PubMed
Summary
This summary is machine-generated.

This study reveals negative effective mass and density in polymer-based systems due to entropic forces. These phenomena are temperature-dependent and emerge in core-shell mechanical systems.

Keywords:
core-shell systementropic forcenegative densitynegative masspolymer springtemperature dependence

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Area of Science:

  • Physics
  • Materials Science
  • Polymer Science

Background:

  • Polymer elasticity is partially of entropic origin, driven by the tendency to reach more probable states.
  • Entropic forces are temperature-dependent, influencing material properties.
  • Negative effective mass and density are unusual phenomena with potential applications.

Purpose of the Study:

  • To investigate the emergence of negative effective mass and density in systems driven by entropic elastic forces.
  • To analyze the temperature dependence of these phenomena in polymer-based core-shell systems.
  • To elucidate the vibrational properties, including optical and acoustical branches.

Main Methods:

  • Modeling core-shell mechanical systems with polymer springs.
  • Calculating temperature-dependent effective mass and density.
  • Analyzing resonance effects when external force frequency approaches eigen-frequency.
  • Investigating vibrational modes in chains of core-shell units.

Main Results:

  • Negative effective mass arises as a resonance effect in core-shell systems with polymer springs.
  • Effective mass and density are shown to be temperature-dependent.
  • Optical and acoustical vibration branches were elucidated.
  • Negative mass and density are attainable by varying system temperature.

Conclusions:

  • Entropic forces in polymer springs can lead to negative effective mass and density.
  • Temperature variation is key to achieving these negative properties.
  • The findings are relevant for understanding and designing advanced mechanical systems.