#WHAT VISCOSITY FULL#

To warm your hands by rubbing them together in wintertime. This is the familiar dynamic friction you use Heat instead of adding to the bookвЂ™s kinetic energy. The gravitational potential energy the sliding book is losing is ending up as Of atoms are constantly colliding, loose bonds are forming and breaking, some atomsДЄ lot of atomic and molecular vibration at the surface. This must be because in the area of contact with the desk the two sets

#WHAT VISCOSITY FULL#

But thereвЂ™s still some friction:Д®xperimentally, the book does not have the full acceleration the component of gravity On tilting the desk more, the static frictional force turnsД«egins to slide. Parallel surfaces of transparent material separated by distances comparable to the (Incidentally, if two surfaces which really are flat at the atomic level are putДЄ real challenge in the optical telecommunications industry, where wavelengthДЇilters (called etalons) are manufactured by having extremely flat, highly The area of вЂњtrue contactвЂќ extra pressure makes little difference. If the normal force is doubled (by addingДЄnother book, say) the tiny area of contact between the bottom book and theДЄrea of atomic contact increases linearly This small area determines the frictional force. That there is only atom-atom interaction between the solids over a small area, and what happens in The stresses within that tiny area are large, the materials distort plasticallyД«e very complex, depending on the materials involved, but the bottom line is Tiny fraction of the common surface is really in contact at the atomic level. Scale: when two flat looking solid surfaces are pushed together, in fact only a By the way, the first appearance of FВ being proportional to NВ is in the notebooks of Leonardo da Vinci.) The book begins to slide, and ОјВ is the coefficient of friction. On a microscopic scale, this staticДЇrictional force is from fairly short range attractions between molecules onД«ut if thatвЂ™s true, why does doubling the normal force double thisДЇrictional force? (Recall F = Ој N ,В where NВ is the normal force, FВ is the limiting frictional force just before Parallel to the surface in the uphill direction. Rest, the вЂњdownhillвЂќ component of gravity is balanced by a frictional force The surface is exactly balanced by the normal force, and if the book is at The gravitational component perpendicular to To the surface and one parallel to the surface (downhill). To visualize the vertical gravitational force as made up of a component normal Springiness of the desktop, slightly compressed by the weight of theД«ook.) When the desk is tilted, itвЂ™s best The desk surface pushing the book in the direction normal to the desk Sort of attractive force between the book and the desk to hold the book fromД«ook: gravity is pulling it vertically down, and there is a вЂњnormal forceвЂќ of At a certain angle of tilt, the book begins to Quick Review of Friction Between SolidsДЇriction: suppose a book is lying on your desk, and you tilt the desk. Which is a measure of the rate of transfer of heat from a warm place to aД¬ooler place. Looked at in this second way, it is analogous to thermal conductivity, Unraveled at the molecular level, but there the explanations turn out to beДЄs will become clear later, the coefficient of viscosity О·В can be viewed in two rather different (but ofД¬ourse consistent) ways: it is a measure of how much heat is generated when fasterДЇluid is flowing by slower fluid, but it is also a measure of the rate of transfer of momentum from the Also, the viscosity of a gas doesnвЂ™t depend in Values vary: for example, on raising the temperature, the viscosity of liquids decreases, that of gases increases. Microscopic picture can give at least a qualitative understanding of how these Values for different fluids and temperatures, and demonstrate how the

Going on to fluids, weвЂ™ll give theДefinition of the coefficient of viscosity for liquids and gases, give some Significance of the coefficient of friction ОјВ in the familiar equation F = Ој N. To begin with, weвЂ™ll review the molecular picture of friction Solids and/or liquids sliding past each other as seen on the molecular scale. Transfer takes place, it is essential to have some picture, however crude, of Viscosity transforms kinetic energy of (macroscopic) motion into heatДЄt the molecular level, so to have any understanding of how this energy Viscosity is, essentially, fluid friction. Michael Fowler Introduction: Friction at the Molecular Level Previous index next Viscosity I: Liquid Viscosity

What viscosity