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Friction is the force that opposes the relative motion or tendency toward such motion of two surfaces in contact. It is not a fundamental force, as it is made up of electromagnetic forces between atoms. When contacting surfaces move relative to each other, the friction between the two objects converts kinetic energy into thermal energy, or heat. Friction between solid objects and fluids (gases or liquids) is called drag. In physics, force is an influence that may cause a body to accelerate. ...
A fundamental interaction is a mechanism by which particles interact with each other, and which cannot be explained by another more fundamental interaction. ...
In physics, the electromagnetic force is the force that the electromagnetic field exerts on electrically charged particles. ...
Kinetic energy is the energy by virtue of the motion of an object. ...
In physics, heat, symbolized by Q, is defined as energy in transit. ...
An object falling through a gas or liquid experiences a force in direction opposite to its motion. ...
Classical approximation
The classical approximation of the force of friction between two solid surfaces is known as Coulomb friction, named after Charles-Augustin de Coulomb. The equation is: Portrait of Coulomb Charles Augustin Coulomb (June 14, 1736 – August 23, 1806) was a French physicist. ...
- ,
where- - μ is the coefficient of friction, which is an empirical property of the contacting materials,
- N is the normal force exerted between the surfaces, and
- Ff is either the force exerted by friction, or the maximum possible magnitude of this force.
For surfaces in relative motion, μ is the coefficient of kinetic friction (see below), the Coulomb friction is equal to Ff, and the frictional force on each surface is exerted in the direction opposite to its motion relative to the other surface. The resistance to lateral motion when one attempts to slide the surface of one object over another surface is called friction or traction. ...
Fn represents the normal force. ...
For surfaces at rest relative to each other, μ is the coefficient of static friction (generally larger than its kinetic counterpart), the Coulomb friction may take any value from zero up to Ff, and the direction of the frictional force on a surface is opposite to the motion that surface would experience in the absence of friction. Thus, in the static case, the frictional force is exactly what it must be in order to prevent motion between the surfaces; it balances the net force tending to cause such motion. In this case, rather than providing an estimate of the actual frictional force, the Coulomb approximation provides a threshold value for this force, above which sliding would commence.
This approximation mathematically follows from the assumptions that surfaces are in atomically close contact only over a small fraction of their overall area, that this contact area is proportional to the normal force (until saturation, which takes place when all area is in atomic contact), and that frictional force is proportional to contact area. Such reasoning aside, however, the approximation is fundamentally an empirical construction. Rather than a physical law, it is a rule of thumb describing the approximate outcome of an extremely complicated physical interaction. The strength of the approximation is its simplicity and versatility--though in general the relationship between normal force and frictional force is not exactly linear (and so the frictional force is not entirely independent of the contact area of the surfaces), the Coulomb approximation is an adequate representation of friction for the analysis of many physical systems. Please wikify (format) this article as suggested in the Guide to layout and the Manual of Style. ...
Fn represents the normal force. ...
Look up Saturation in Wiktionary, the free dictionary. ...
Coefficient of friction -
The coefficient of friction (also known as the frictional coefficient) is a dimensionless scalar value which describes the ratio of the force of friction between two bodies and the force pressing them together. The coefficient of friction depends on the materials used -- for example, ice on steel has a low coefficient of friction (the two materials slide past each other easily), while rubber on pavement has a high coefficient of friction (the materials do not slide past each other easily). Coefficients of friction range from near zero to greater than one - under good conditions, a tire on concrete may have a coefficient of friction of 1.7. The resistance to lateral motion when one attempts to slide the surface of one object over another surface is called friction or traction. ...
In physics, a scalar is a simple physical quantity that does not depend on direction, and therefore does not depend on the choice of a coordinate system. ...
In physics, force is an influence that may cause a body to accelerate. ...
When the surfaces are adhesive, Coulomb friction becomes a very poor approximation (for example, Scotch tape resists sliding even when there is no normal force, or a negative normal force). In this case, the frictional force may depend strongly on the area of contact. Some drag racing tires are adhesive in this way. An adhesive is a compound that adheres or bonds two items together. ...
Scotch Tape denotes the line of adhesive tapes manufactured by 3M as part of the companys Scotch brand. ...
This article or section does not cite its references or sources. ...
The force of friction is always exerted in a direction that opposes movement (for kinetic friction) or potential movement (for static friction) between the two surfaces. For example, a curling stone sliding along the ice experiences a kinetic force slowing it down. For an example of potential movement, the drive wheels of an accelerating car experience a frictional force pointing forward; if they did not, the wheels would spin, and the rubber would slide backwards along the pavement. Note that it is not the direction of movement of the vehicle they oppose, it is the direction of (potential) sliding between tire and road. Curling is a precision team sport similar to bowls or bocce, played on a rectangular sheet of prepared ice by two teams of four players each, using heavy polished granite stones which players slide down the ice towards a target area called the house. ...
The coefficient of friction is an empirical measurement -- it has to be measured experimentally, and cannot be found through calculations. Rougher surfaces tend to have higher values. Most dry materials in combination have friction coefficient values between 0.3 and 0.6. Values outside this range are rarer, but Teflon, for example, can have a coefficient as low as 0.04. A value of zero would mean no friction at all, an elusive property--even Magnetic levitation vehicles have drag. Rubber in contact with other surfaces can yield friction coefficients from 1.0 to 2.0. Empirical is an adjective often used in conjunction with science, both the natural and social sciences, which means an observation or experiment based upon experience that is capable of being verified or disproved. ...
Various meters Measurement is the estimation or determination of extent, dimension or capacity, usually in relation to some standard or unit of measurement. ...
In the scientific method, an experiment (Latin: ex-+-periri, of (or from) trying), is a set of actions and observations, performed in the context of solving a particular problem or question, to support or falsify a hypothesis or research concerning phenomena. ...
Teflon is polytetrafluoroethylene (PTFE), a polymer of fluorinated ethylene. ...
Levitating pyrolytic carbon Magnetic levitation, maglev, or magnetic suspension is a method by which an object is suspended above another object with no support other than magnetic fields. ...
Transrapid at the Emsland test facility in Germany Transrapid maglev train in Shanghai Inside the Shanghai Transrapid maglev Inside the Shanghai Transrapid maglev VIP section Magnetic levitation transport, or maglev, is a form of transportation that suspends, guides and propels vehicles via electromagnetic force. ...
Look up Drag in Wiktionary, the free dictionary. ...
Types of friction
Static friction Static friction occurs when the two objects are not moving relative to each other (like a book on a desk). The coefficient of static friction is typically denoted as μs. The initial force to get an object moving is often dominated by static friction. The static friction is in most cases higher than the kinetic friction. Rolling friction occurs when one object "rolls" on another (like a car's wheels on the ground). This is classified under static friction because the patch of the tire in contact with the ground, at any point while the tire spins, is stationary relative to the ground. The coefficient of rolling friction is typically denoted as μr. Rolling friction is the friction that occurs when an object (e. ...
Limiting friction is the maximum value of static friction, or the force of friction that acts when a body is just on the verge of motion on a surface.
Kinetic friction Kinetic (or dynamic) friction occurs when two objects are moving relative to each other and rub together (like a sled on the ground). The coefficient of kinetic friction is typically denoted as μk, and is usually less than the coefficient of static friction. From the mathematical point of view, however, the difference between static and kinetic friction is of minor importance: Let us have a coefficient of friction which depends on the sliding velocity and is such that its value at 0 (the static friction μs ) is the limit of the kinetic friction μk for the velocity tending to zero. Then a solution of the contact problem with such Coulomb friction solves also the problem with the original μk and any static friction greater than that limit.
Since friction is exerted in a direction that opposes movement, kinetic friction usually does negative work, typically slowing something down. There are exceptions however, if the surface itself is under acceleration. One can see this by placing a heavy box on a rug, then pulling on the rug quickly. In this case, the box slides backwards relative to the rug, but moves forward relative to the floor. Thus, the kinetic friction between the box and rug accelerates the box in the same direction that the box moves, doing positive work.
Examples of kinetic friction:
- Sliding friction is when two objects are rubbing against each other. Putting a book flat on a desk and moving it around is an example of sliding friction
- Fluid friction is the friction between a solid object as it moves through a liquid or a gas. The drag of air on an airplane or of water on a swimmer are two examples of fluid friction.
Sliding friction is when two objects are rubbing against each other. ...
Fluid friction is the friction between a solid object and a fluid (a liquid or gas) it is moving through. ...
Reducing friction
Devices Devices such as wheels, ball bearings or rollers can change sliding friction into much smaller rolling friction. A 4 point contact ball bearing A ball bearing is a common type of rolling-element bearing, a kind of bearing. ...
Techniques One technique used by railroad engineers is to back up the train to create slack in the linkages between cars. This allows the train to pull forward and only take on the static friction of one car at a time, instead of all cars at once, thus spreading the static frictional force out over time. Determining the Coefficient of Friction. ...
Lubricants A common way to reduce friction is by using a lubricant, such as oil or water, which is placed between the two surfaces, often dramatically lessening the coefficient of friction. The science of friction and lubrication is called tribology. Lubricant technology is when lubricants are mixed with the application of science, especially to industrial or commercial objectives. It has been suggested that this article or section be merged into Lubrication. ...
Tribology is the science and technology of friction, lubrication, and wear, derived from the Greek tribo meaning I rub. Formally defined, it is the science and technology of interacting surfaces in relative motion and all practices related thereto. ...
Superlubricity, a recently-discovered effect, has been observed in graphite: it is the substantial decrease of friction between two sliding objects, approaching zero levels (a very small amount of frictional energy would still be dissipated). Superlubricity is a certain phenomenon in which friction can vanish almost completely. ...
Graphite (named by Abraham Gottlob Werner in 1789, from the Greek γÏαφειν: to draw/write, for its use in pencils) is one of the allotropes of carbon. ...
Lubricants to overcome friction need not always be thin, turbulent fluids or powdery solids such as graphite and talc; acoustic lubrication actually uses sound as a lubricant. Talc block Talcum Powder Talc is a mineral composed of hydrated magnesium silicate with the chemical formula H2Mg3(SiO3)4 or Mg3Si4O10(OH)2. ...
// Definition Acoustic/sonic lubrication occurs when sound (measurable in a vacuum by placing a microphone on one element of the sliding system) permits vibration to introduce separation between the sliding faces. ...
Energy of friction According to the law of conservation of energy, no energy is destroyed due to friction, though it may be lost to the system of concern. Energy is transformed from other forms into heat. A sliding hockey puck comes to rest due to friction as its kinetic energy changes into heat. Since heat quickly dissipates, many early philosophers, including Aristotle, wrongly concluded that moving objects lose energy without a driving force. Conservation of energy states that the total amount of energy in an isolated system remains constant, although it may change forms (for instance, friction turns kinetic energy into thermal energy). ...
Aristotle (Greek: Aristotélēs) (384 BC – March 7, 322 BC) was a Greek philosopher, a student of Plato and teacher of Alexander the Great. ...
When an object is pushed along a surface, the energy converted to heat is given by:
-
-
- where
- N is the normal force,
- μk is the coefficient of kinetic friction,
- x is the coordinate along which the object transverses.
Physical deformation is associated with friction. While this can be beneficial, as in polishing, it is often a problem, as the materials are worn away, and may no longer hold the specified tolerances. Fn represents the normal force. ...
Tolerance in Final Fantasy is an allowance, given as a permissible range, in the nominal dimension or value specification of a manufactured object. ...
The work done by friction can translate into deformation and heat that in the long run may affect the surface's specification and the coefficient of friction itself. Friction can in some cases cause solid materials to melt. In physics, melting is the process of heating a solid substance to a point (called the melting point) where it turns into a liquid. ...
See also In the article vector quantities are written in bold whereas scalar ones are in italics. ...
Rolling resistance, sometimes called rolling friction, is the resistance that occurs when an object (e. ...
Tribology is the science and technology of friction, lubrication, and wear, derived from the Greek tribo meaning I rub. Formally defined, it is the science and technology of interacting surfaces in relative motion and all practices related thereto. ...
Traction usually refers to friction between a drive member and the surface it runs on, where friction is used to provide motion. ...
A tire or tyre (see spelling differences and etymological origins) is a device covering the circumference of a wheel. ...
For other uses, see Collision (disambiguation). ...
References - Tipler, Paul (1998). Physics for Scientists and Engineers: Vol. 1, 4th ed., W. H. Freeman. ISBN 1-57259-492-6.
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