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# Topic: Van der Waals force

###### In the News (Tue 21 May 13)

 Van der Waals force - Wikipedia, the free encyclopedia Forces that deal with fixed or angle averaged dipoles (Keesom forces) and free or rotation dipoles (Debye forces) as well as shifts in electron cloud distribution (London Forces) are named after the Dutch chemist Johannes Diderik van der Waals who first documented these interactions. Van der Waals forces are responsible for certain cases of pressure broadening (Van der Waals broadening) of spectral lines. The London-Van der Waals force is related to the Casimir effect for dielectric media, the former the microscopic description of the latter bulk property. en.wikipedia.org /wiki/Van_der_Waals_force   (817 words)

 Van der Waals radius   (Site not responding. Last check: 2007-11-05) The van der Waals radius of an atom is the radius of an imaginary hard sphere which can be used to model the atom for many purposes. Van der Waals radii are determined from measurements of atomic spacing between pairs of unbonded atoms in crystals. The van der Waals radius is named after Johannes Diderik van der Waals, winner of the 1910 Nobel Prize in Physics. uncover.us /en/wikipedia/v/va/van_der_waals_radius.html   (332 words)

 Encyclopedia: Van der Waals force van der Waals Johannes Diderik Van der Waals (November 23, 1837 â€“ March 8, 1923) was a Dutch scientist famous for his work on the equation of state for gases and liquids, for which he won the Nobel Prize in physics in 1910. The van der Waals radius of an ((physics and chemistry) the smallest component of an element having the chemical properties of the element) atom is the radius of an imaginary hard (A particular environment or walk of life) sphere which can be used to model the atom for many purposes. Van der Waals radii are determined from measurements of atomic spacing between pairs of unbonded atoms in (A crystalline element used as a component in various electronic devices) crystals. www.nationmaster.com /encyclopedia/Van-der-Waals-force   (941 words)

 Van der Waals equation - Wikipedia, the free encyclopedia The van der Waals equation is an equation of state for a fluid composed of particles that have a non-zero size and a pairwise attractive inter-particle force (such as the van der Waals force.) It was derived by Johannes Diderik van der Waals in 1873, based on a modification of the ideal gas law. The derivation of the van der Waals equation begins with the equation of state of an ideal gas, which is composed of non-interacting point particles: Although the material constants a and b in the usual form of the van der Waals equation differs for every single gas/fluid considered, the equation can be recast into an invariant form applicable to all gases/fluids. www.wikipedia.org /wiki/Van_der_Waals_equation   (910 words)

 Clarkson U. | CRCD | ME 637 | Particle Adhesion The London-van der Waals force, which is generally attractive in nature, is a short range force and decays rapidly to zero away from a surface. The origin of the London-van der Waals force lies in the instantaneous dipole generated by the fluctuation of electron cloud surrounding the nucleus of electrically neutral atoms. In Table 1 values for van der Waals force for a number of materials are listed and the values of van der Waals force is compared with the Stokes drag force acting on a particle that is moving with a velocity of 1 m/s in aid and in water. www.clarkson.edu /projects/crcd/me637/notes/particle_adhesion/particle_adhesion_page1.html   (236 words)

 KNAW > Van der Waals > Scientists > Van der Waals Johannes Diderik Van der Waals (1837-1923) was born in Leiden, the oldest of the ten children of a carpenter. In the thesis, he introduced the concepts of molecular volume and molecular attraction (presently known as the Van der Waals force), and described the behavior of condensing gases and criticality by means of the famous Van der Waals equation. Van der Waals was elected to the Royal Netherlands Academy of Arts and Sciences (KNAW) in 1875, and to the Holland Society of Sciences and Humanities (HMW) in 1878. www.knaw.nl /waals/waals.html   (1050 words)

 Clarkson U. | CRCD | ME 637 | Particle Adhesion | van der Waals Force Values of van der Waals, surface tension, added mass, drag and Basset forces acting on a sphere of different sizes moving with a velocity of 10 m/s are shown in Table 2. Among the hydrodynamic forces, drag is the dominating force and the virtual mass and the Basset forces are negligibly small. In water, the surface tension force is absent and the drag force acting on large particles beomes comparable with the van der Waals adhesion force. www.clarkson.edu /projects/crcd/me637/notes/particle_adhesion/particle_adhesion_page2.html   (124 words)

 Van der Waals radius - Encyclopedia, History, Geography and Biography Particularly useful and well known is the van der Waals equation of state: $\left \left(P + \frac\left\{a\right\}\left\{\tilde\left\{V\right\}^2\right\}\right\right) \left(\tilde\left\{V\right\} - b\right) = RT$, where a and b are adjustable parameters determined from experimental measurements carried out on actual gases. The van der Waals volume of a molecule or system of molecules is the sum of the union of the van der Waals spheres of the atoms in the system. Van der Waals radius, van der Waals volume, See also, References, External links and Chemical properties. www.arikah.com /encyclopedia/Van_der_Waals_radius   (416 words)

 General Chemistry Online: FAQ: Liquids: What are van der Waals forces? Van der Waals forces are much weaker than chemical bonds, and random thermal motion around room temperature can usually overcome or disrupt them. Van der Waals' forces include all intermolecular forces that act between electrically neutral molecules. However, they are usually weaker than the permanent forces that they are usually only invoked to explain intermolecular forces between nonpolar molecules or noble gas atoms. antoine.frostburg.edu /chem/senese/101/liquids/faq/h-bonding-vs-london-forces.shtml   (836 words)

 Theory and Simulation of SPM The force most commonly associated with atomic force microscopy is an interatomic force called the van der Waals force. The dependence of the van der Waals force upon the distance between the tip and the sample is shown in Figure 3. In the non-contact regime, the cantilever is held on the order of tens to hundreds of angstroms from the sample surface, and the interatomic force between the cantilever and sample is attractive (largely a result of the long-range van der Waals interactions). invsee.asu.edu /nmodules/spmmod/afm.html   (263 words)

 van der Waals forces --  Encyclopædia Britannica The forces are named for the Dutch physicist Johannes van der Waals, who in 1873 first postulated these intermolecular forces in developing a theory to account for the properties of real gases. The weak attractive forces between atoms or molecules, van der Waals forces, were named in honor of Johannes van der Waals, a Dutch physicist. Van der Waals received the Nobel prize in physics in 1910 for his research on the gaseous and liquid states of matter in which he developed a formula for the continuity of all gases, the van der Waals equation. www.britannica.com /eb/article-9074766   (851 words)

 9.2.1 In dry or vacuum environments, adhesion forces between <100 micron diameter particles and surfaces (nanorobot and other) separated by 100 nm or less are usually dominated by van der Waals interactions. Van der Waals forces also depend upon the roughness of the surface. This result suggests that forces on the order of 10-100 pN must be applied to mobile nanoscale components inside mechanical nanodevices in order to overcome static van der Waals adhesion that arises due to the contact proximity of parts within the structure. www.nanomedicine.com /NMI/9.2.1.htm   (637 words)

 Glossary   (Site not responding. Last check: 2007-11-05) The centripetal force on an object moving in a curved path is the inward force that must be exerted to produce this motion. A field of force is a region of altered space (for example, around a mass, an electric charge, a magnet) that exerts a force on appropriate objects in that region. The magnetic force between two moving charges is a modification of the electric force between them due to their motion; it is a relativistic effect. www.dac.neu.edu /physics/b.maheswaran/phy1121/data/glos/glossary.htm   (8264 words)

 Van der Waals Interaction The final contribution to the force is the van der Waals interaction. In fact, the macroscopic contribution to the van der Waals force is the same in each of the three systems described below, as it depends only on the tip-surface separation, macroscopic sphere radius, cone-angle and Hamaker constant of the system. The force exerted on one atom due to this interaction at characteristic tip-sample distances is several orders of magnitude smaller than the force between macroscopic tip and substrate. www.fyslab.hut.fi /~asf/physics/thesis1/node80.html   (314 words)

 JOHANNES VAN DER WAALS. Free term papers for college, book reports and research papers. Welcome to EZ Term Papers Biography Johannes Diderik van der Waals was born on November 23, 1837 in Leyden, located in The Netherlands.His parents were Jacobus van der Waals, a carpenter and Elisabeth van den Burg. Van der Waals forces scientific definition is, a term used to describe the weakest intermolecular attractions; these include dispersion forces and dipole interactions. Hydrogen bonding by scientific is a relatively strong intermolecular force in which a hydrogen atom that is covalently bonded to a very electronegative atom is also weakly bonded to an unshared electron pair of an electronegative atom in the same molecule or one nearby. www.eztermpapers.com /essay/009492.html   (2183 words)

 Spiders make best ever Post-it notes The paper reveals that the force these spiders use to stick to surfaces is the van der Waals force, which acts between individual molecules that are within a nanometre of each other (a nanometre is about ten thousand times smaller than the width of a human hair). The total van der Waals force on the spider's feet is very strong, but it is the sum of many very small forces on each molecule. This particular electrostatic attraction is called the van der Waals force, and is in some ways similar to the magnetic attraction between north and south poles of magnets. www.eurekalert.org /pub_releases/2004-04/iop-smb041504.php   (1198 words)

 Intermolecular Attractions or van der Waals Forces   (Site not responding. Last check: 2007-11-05) Van der Waals forces aren’t just important when dealing with gases; these forces are important in understanding the bulk properties of the other states of matter, too. There are three types of van der Waals forces that may occur in pure substances: induced dipole attractions, dipole-dipole attractions, and hydrogen bonds. The rank for increasing induced dipole force is water < hydrogen sulfide < hydrogen selenide, because induced dipole force increases as the size of the molecule increases. www.chemprofessor.com /imf.htm   (1089 words)

 Intermolecular force - Wikipedia, the free encyclopedia These are fundamentally electrostatic interactions (ionic interactions, hydrogen bond, dipole-dipole interactions) or electrodynamic interactions (van der Waals/London forces). Hydrogen bonds between hydrogen atoms and nitrogen atoms of adjacent base pairs provide the intermolecular force that bind together the two strands in a molecule of DNA. Also called London forces, instantaneous dipole effects or Van der Waals forces, these involve the attraction between temporarily induced dipoles in nonpolar molecules (often disappear within a second). en.wikipedia.org /wiki/Intermolecular_force   (494 words)

 Theory and Simulation of SPM In addition to the repulsive van der Waals force described above, two other forces are generally present during contact AFM operation: a capillary force exerted by the thin water layer often present in an ambient environment, and the force exerted by the cantilever itself. The total force that the tip exerts on the sample is the sum of the capillary plus cantilever forces, and must be balanced by the repulsive van der Waals force for contact AFM. The magnitude of the total force exerted on the sample varies from 10-8 (with the cantilever pulling away from the sample almost as hard as the water is pulling down the tip - see Force vs. distance curves), to the more typical operating range of 10-7 to 10-6N. invsee.asu.edu /nmodules/spmmod/cfm.html   (899 words)

 V - Glossary of chemical terms Van der Waals' equation is an equation of state for fluids which takes the form: Van derWaals' force is the weak attractive force between two molecules which arises from electric dipole interactions. The weber is the magnetic flux which, linking a circuit of one turn, produces in it an electromotive force of one volt as it is reduced to zero at a uniform rate in one second (Wb = V∙s). www.ktf-split.hr /periodni/en/abc/v.html   (435 words)

 intermolecular bonding - van der Waals forces   (Site not responding. Last check: 2007-11-05) The forces of attraction which hold an individual molecule together (for example, the covalent bonds) are known as intramolecular attractions. Dispersion forces (one of the two types of van der Waals force we are dealing with on this page) are also known as "London forces" (named after Fritz London who first suggested how they might arise). Dispersion forces, for example, were described by London in 1930; dipole-dipole interactions by Keesom in 1912. www.chemguide.co.uk /atoms/bonding/vdw.html   (1436 words)

 Dorlands Medical Dictionary the force which, by reason of differences in potential, causes a flow of electricity from one place to another, giving rise to an electric current; it is measured in volts. the unit of force exerted on a resting body that is equal to the force on it due to gravity. van der Waals f.’s the relatively weak, short-range forces of attraction existing between atoms and molecules and arising from brief shifts of orbital electrons on one side of the atom or molecule and the corresponding electron shifts in adjacent molecules; it results in the attraction of nonpolar organic compounds to each other. www.mercksource.com /pp/us/cns/cns_hl_dorlands.jspzQzpgzEzzSzppdocszSzuszSzcommonzSzdorlandszSzdorlandzSzdmd_f_13zPzhtm   (3747 words)

 van der Waals   (Site not responding. Last check: 2007-11-05) The term ‘van der Waals’ force’ has sometimes been used to mean only forces involving temporary dipoles, and this is not correct. The van der Waals forces, that is forces between molecules having closed shells, consist of several types of interaction. The dispersion effect or London force (temporary dipole-induced dipole): This is the only force of interaction in non-polar molecules, and arises from a temporary dipole inducing a complementary dipole in an adjacent molecule. www.rod.beavon.clara.net /vander.htm   (443 words)

 Chemical Bonds   (Site not responding. Last check: 2007-11-05) Water molecules in liquid water are attracted to each other by electrostatic forces, and these forces have been described as van der Waals forces or van der Waals bonds. Even though the water molecule as a whole is electrically neutral, the distribution of charge in the molecule is not symmetrical and leads to a dipole moment - a microscopic separation of the positive and negative charge centers. Even nonpolar molecules experience some van der Waals bonding, which can be attributed to their being polarizable. hyperphysics.phy-astr.gsu.edu /hbase/chemical/waal.html   (241 words)

 From the Cover: Evidence for van der Waals adhesion in gecko setae -- Autumn et al. 99 (19): 12252 -- Proceedings of ... Therefore, we reject the hypothesis that wet, capillary interactions are necessary for gecko adhesion in favor of the van der Waals hypothesis. force between the probe and the synthetic spatula was measured. The strong adhesion between the hydrophobic surface of the gecko's toes and the hydrophobic GaAs surfaces demonstrates that the mechanism of adhesion in geckos is van der Waals force. www.pnas.org /cgi/content/full/99/19/12252   (3435 words)

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