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Related Concept Videos

Density00:56

Density

Density is an important characteristic of substances, crucial in determining whether an object sinks or floats in a fluid. Its SI unit is kg/m3, and its cgs unit is g/cm3. The density of an object helps in identifying its composition, and also reveals information about the phase of the matter and its substructure. The densities of liquids and solids are roughly comparable, consistent with the fact that their atoms are in close contact. However, gases have much lower densities than liquids and...
Surface Tension of Fluid01:22

Surface Tension of Fluid

Surface tension is a fundamental property of fluids, occurring at the boundary between a liquid and a gas or between two immiscible liquids. This phenomenon arises from the cohesive forces between molecules at the fluid's surface, creating an effect similar to a stretched elastic membrane. Inside each fluid, molecules are equally attracted in all directions by neighboring molecules, but surface molecules experience a net inward force, resulting in surface tension.
Surface tension varies with...
Pressure Variation in a Fluid at Rest01:11

Pressure Variation in a Fluid at Rest

In a fluid at rest, the pressure at any point beneath the fluid surface depends solely on the depth, not on the container's shape or size. This principle, known as hydrostatic pressure, arises because, in stationary fluids, there is no acceleration, meaning the forces within the fluid balance out. Only vertical forces, caused by the weight of the fluid above, contribute to pressure changes with depth.
When measuring pressure at two different levels within the fluid, the difference in pressure...
States of Water01:23

States of Water

Water exists in any one of the three classical states: solid (ice), liquid (water), and gas (steam or water vapor). The state of water depends on i) the intermolecular forces that draw molecules together and ii) the kinetic energy that leads to movements that pull them apart.
Water freezes when the intermolecular forces are greater than the kinetic energy. Unlike most other substances, water is less dense in its solid state than in its liquid state. This is because each water molecule can form...
Surface Tension, Capillary Action, and Viscosity02:57

Surface Tension, Capillary Action, and Viscosity

Surface Tension
The various IMFs between identical molecules of a substance are examples of cohesive forces. The molecules within a liquid are surrounded by other molecules and are attracted equally in all directions by the cohesive forces within the liquid. However, the molecules on the surface of a liquid are attracted only by about one-half as many molecules. Because of the unbalanced molecular attractions on the surface molecules, liquids contract to form a shape that minimizes the number...
Capillarity in Fluid01:19

Capillarity in Fluid

Capillarity describes the movement of liquid in small spaces without external forces acting on it. The capillarity is driven by surface tension and adhesive interactions between the liquid and surrounding solid surfaces. This effect is often seen in narrow tubes, porous materials, and fine particles.
Surface tension is crucial to capillarity. It results from cohesive forces between liquid molecules at the liquid-air boundary, forming a skin that resists external forces. When the capillary tube...

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An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids
11:03

An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids

Published on: December 4, 2017

Density fluctuations in liquid water.

Niall J English1, John S Tse

  • 1The SEC Strategic Research Cluster and the Centre for Synthesis and Chemical Biology, School of Chemical and Bioprocess Engineering, University College Dublin, Belfield, Dublin 4, Ireland. niall.english@ucd.ie

Physical Review Letters
|March 17, 2011
PubMed
Summary
This summary is machine-generated.

Molecular dynamics simulations reveal that low- and high-density regions in water are transient phenomena. Their existence and duration depend on system size and natural density fluctuations.

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Area of Science:

  • Physical Chemistry
  • Computational Chemistry
  • Materials Science

Background:

  • Liquid water exhibits complex dynamic behavior, including the presence of low- and high-density regions.
  • Understanding these density fluctuations is crucial for characterizing water's unique properties, especially in supercooled states.

Purpose of the Study:

  • To analyze density distributions and fluctuations in liquid water across various system sizes.
  • To investigate the transient nature and spatial extent of low- and high-density regions (LDL and HDL).
  • To determine the influence of system size on the residence times of LDL and HDL.

Main Methods:

  • Large-scale molecular dynamics (MD) simulations were employed to generate water trajectories.
  • Analysis focused on density distributions and fluctuations in systems of varying grid sizes.
  • Residence times and spatial correlations of density variations were calculated.

Main Results:

  • The occurrence of low- and high-density regions (LDL and HDL) in water is transient.
  • The residence times of LDL and HDL are dependent on the size of the simulated system.
  • Density-density correlations have a spatial extent of 7 Å or less, indicating localized fluctuations.

Conclusions:

  • LDL and HDL arise from natural density fluctuations in an equilibrium system.
  • The observed density variations are not permanent but temporary features of liquid water.
  • Bulk water at ambient conditions exhibits a homogenous density, with fluctuations occurring at a local level.