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Friction

Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. Types of friction include dry, fluid, lubricated, skin, and internal.

Friction can have dramatic consequences, as illustrated by the use of friction created by rubbing pieces of wood together to start a fire. Kinetic energy is converted to thermal energy whenever motion with friction occurs, for example when a viscous fluid is stirred. Another important consequence of many types of friction can be wear, which may lead to performance degradation or damage to components.

Friction is a non-conservative force – work done against friction is path dependent. In the presence of friction, some kinetic energy is always transformed to thermal energy, so mechanical energy is not conserved. Friction is not itself a fundamental force. Dry friction arises from a combination of inter-surface adhesion, surface roughness, surface deformation, and surface contamination. The complexity of these interactions makes the calculation of friction from first principles difficult and it is often easier to use empirical methods for analysis and the development of theory.

Types
There are several types of friction:
 * Dry friction is a force that opposes the relative lateral motion of two solid surfaces in contact. Dry friction is subdivided into static friction ("stiction") between non-moving surfaces, and kinetic friction between moving surfaces. With the exception of atomic or molecular friction, dry friction generally arises from the interaction of surface features, known as asperities (see Figure).
 * Fluid friction describes the friction between layers of a viscous fluid that are moving relative to each other.

 * Lubricated friction is a case of fluid friction where a lubricant fluid separates two solid surfaces.

 * Skin friction is a component of drag, the force resisting the motion of a fluid across the surface of a body.
 * Internal friction is the force resisting motion between the elements making up a solid material while it undergoes deformation.

History
Many ancient authors including Aristotle, Vitruvius, and Pliny the Elder, were interested in the cause and mitigation of friction. They were aware of differences between static and kinetic friction with Themistius stating in 350 that "it is easier to further the motion of a moving body than to move a body at rest".

The classic laws of sliding friction were discovered by Leonardo da Vinci in 1493, a pioneer in tribology, but the laws documented in his notebooks were not published and remained unknown. These laws were rediscovered by Guillaume Amontons in 1699 and became known as Amonton's three laws of dry friction. Amontons presented the nature of friction in terms of surface irregularities and the force required to raise the weight pressing the surfaces together. This view was further elaborated by Bernard Forest de Bélidor and Leonhard Euler (1750), who derived the angle of repose of a weight on an inclined plane and first distinguished between static and kinetic friction. John Theophilus Desaguliers (1734) first recognized the role of adhesion in friction. Microscopic forces cause surfaces to stick together; he proposed that friction was the force necessary to tear the adhering surfaces apart. The understanding of friction was further developed by Charles-Augustin de Coulomb (1785). Coulomb investigated the influence of four main factors on friction: the nature of the materials in contact and their surface coatings; the extent of the surface area; the normal pressure (or load); and the length of time that the surfaces remained in contact (time of repose). Coulomb further considered the influence of sliding velocity, temperature and humidity, in order to decide between the different explanations on the nature of friction that had been proposed. The distinction between static and dynamic friction is made in Coulomb's friction law (see below), although this distinction was already drawn by Johann Andreas von Segner in 1758. The effect of the time of repose was explained by Pieter van Musschenbroek (1762) by considering the surfaces of fibrous materials, with fibers meshing together, which takes a finite time in which the friction increases.

John Leslie (1766–1832) noted a weakness in the views of Amontons and Coulomb: If friction arises from a weight being drawn up the inclined plane of successive asperities, why then isn't it balanced through descending the opposite slope? Leslie was equally skeptical about the role of adhesion proposed by Desaguliers, which should on the whole have the same tendency to accelerate as to retard the motion. In Leslie's view, friction should be seen as a time-dependent process of flattening, pressing down asperities, which creates new obstacles in what were cavities before.

In the long course of the development of the law of conservation of energy and of the first law of thermodynamics, friction was recognised as a mode of conversion of mechanical work into heat. In 1798, Benjamin Thompson reported on cannon boring experiments.

Arthur Jules Morin (1833) developed the concept of sliding versus rolling friction.

In 1842, Julius Robert Mayer frictionally generated heat in paper pulp and measured the temperature rise. In 1845, Joule published a paper entitled The Mechanical Equivalent of Heat, in which he specified a numerical value for the amount of mechanical work required to "produce a unit of heat", based on the friction of an electric current passing through a resistor, and on the friction of a paddle wheel rotating in a vat of water.

Osborne Reynolds (1866) derived the equation of viscous flow. This completed the classic empirical model of friction (static, kinetic, and fluid) commonly used today in engineering. In 1877, Fleeming Jenkin and J. A. Ewing investigated the continuity between static and kinetic friction.

In 1907, G.H. Bryan published an investigation of the foundations of thermodynamics, Thermodynamics: an Introductory Treatise dealing mainly with First Principles and their Direct Applications. He noted that for a driven hard surface sliding on a body driven by it, the work done by the driver exceeds the work received by the body. The difference is accounted for by heat generated by friction. Over the years, for example in his 1879 thesis, but particularly in 1926, Planck advocated regarding the generation of heat by rubbing as the most specific way to define heat, and the prime example of an irreversible thermodynamic process.

The focus of research during the 20th century has been to understand the physical mechanisms behind friction. Frank Philip Bowden and David Tabor (1950) showed that, at a microscopic level, the actual area of contact between surfaces is a very small fraction of the apparent area. This actual area of contact, caused by asperities increases with pressure. The development of the atomic force microscope (ca. 1986) enabled scientists to study friction at the atomic scale, showing that, on that scale, dry friction is the product of the inter-surface shear stress and the contact area. These two discoveries explain Amonton's first law (below); the macroscopic proportionality between normal force and static frictional force between dry surfaces.

Laws of dry friction
The elementary property of sliding (kinetic) friction were discovered by experiment in the 15th to 18th centuries and were expressed as three empirical laws:
 * Amontons' First Law: The force of friction is directly proportional to the applied load.
 * Amontons' Second Law: The force of friction is independent of the apparent area of contact.
 * Coulomb's Law of Friction: Kinetic friction is independent of the sliding velocity.

Dry friction
Dry friction resists relative lateral motion of two solid surfaces in contact. The two regimes of dry friction are 'static friction' ("stiction") between non-moving surfaces, and kinetic friction (sometimes called sliding friction or dynamic friction) between moving surfaces.

Coulomb friction, named after Charles-Augustin de Coulomb, is an approximate model used to calculate the force of dry friction. It is governed by the model: $$F_\mathrm{f} \leq \mu F_\mathrm{n},$$ where
 * $$F_\mathrm{f}$$ is the force of friction exerted by each surface on the other. It is parallel to the surface, in a direction opposite to the net applied force.
 * $$\mu$$ is the coefficient of friction, which is an empirical property of the contacting materials,
 * $$F_\mathrm{n}$$ is the normal force exerted by each surface on the other, directed perpendicular (normal) to the surface.

The Coulomb friction $$F_\mathrm{f}$$ may take any value from zero up to $$\mu F_\mathrm{n}$$, and the direction of the frictional force against 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 motion would commence. This maximum force is known as traction.

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.

Normal force

The normal force is defined as the net force compressing two parallel surfaces together, and its direction is perpendicular to the surfaces. In the simple case of a mass resting on a horizontal surface, the only component of the normal force is the force due to gravity, where $$N=mg\,$$. In this case, conditions of equilibrium tell us that the magnitude of the friction force is zero, $$F_f = 0$$. In fact, the friction force always satisfies $$F_f\le \mu N$$, with equality reached only at a critical ramp angle (given by $$\tan^{-1}\mu$$) that is steep enough to initiate sliding.

The friction coefficient is an empirical (experimentally measured) structural property that depends only on various aspects of the contacting materials, such as surface roughness. The coefficient of friction is not a function of mass or volume. For instance, a large aluminum block has the same coefficient of friction as a small aluminum block. However, the magnitude of the friction force itself depends on the normal force, and hence on the mass of the block.

Depending on the situation, the calculation of the normal force $$N$$ might include forces other than gravity. If an object is on a and subjected to an external force $$P$$ tending to cause it to slide, then the normal force between the object and the surface is just $$N = mg + P_y$$, where $$mg$$ is the block's weight and $$P_y$$ is the downward component of the external force. Prior to sliding, this friction force is $$F_f = -P_x$$, where $$P_x$$ is the horizontal component of the external force. Thus, $$F_f \le \mu N$$ in general. Sliding commences only after this frictional force reaches the value $$F_f = \mu N$$. Until then, friction is whatever it needs to be to provide equilibrium, so it can be treated as simply a reaction.

If the object is on a such as an inclined plane, the normal force from gravity is smaller than $$mg$$, because less of the force of gravity is perpendicular to the face of the plane. The normal force and the frictional force are ultimately determined using vector analysis, usually via a free body diagram.

In general, process for solving any statics problem with friction is to treat contacting surfaces tentatively as immovable so that the corresponding tangential reaction force between them can be calculated. If this frictional reaction force satisfies $$F_f \le \mu N$$, then the tentative assumption was correct, and it is the actual frictional force. Otherwise, the friction force must be set equal to $$F_f = \mu N$$, and then the resulting force imbalance would then determine the acceleration associated with slipping.

Coefficient of friction
The coefficient of friction (COF), often symbolized by the Greek letter μ, is a dimensionless scalar value which equals the ratio of the force of friction between two bodies and the force pressing them together, either during or at the onset of slipping. The coefficient of friction depends on the materials used; for example, ice on steel has a low coefficient of friction, while rubber on pavement has a high coefficient of friction. Coefficients of friction range from near zero to greater than one. The coefficient of friction between two surfaces of similar metals is greater than that between two surfaces of different metals; for example, brass has a higher coefficient of friction when moved against brass, but less if moved against steel or aluminum.

For surfaces at rest relative to each other, $$\mu = \mu_\mathrm{s}$$, where $$\mu_\mathrm{s}$$ is the coefficient of static friction. This is usually larger than its kinetic counterpart. The coefficient of static friction exhibited by a pair of contacting surfaces depends upon the combined effects of material deformation characteristics and surface roughness, both of which have their origins in the chemical bonding between atoms in each of the bulk materials and between the material surfaces and any adsorbed material. The fractality of surfaces, a parameter describing the scaling behavior of surface asperities, is known to play an important role in determining the magnitude of the static friction.

For surfaces in relative motion $$\mu = \mu_\mathrm{k}$$, where $$\mu_\mathrm{k}$$ is the coefficient of kinetic friction. The Coulomb friction is equal to $$F_\mathrm{f}$$, and the frictional force on each surface is exerted in the direction opposite to its motion relative to the other surface.

Arthur Morin introduced the term and demonstrated the utility of the coefficient of friction. 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 effective values. Both static and kinetic coefficients of friction depend on the pair of surfaces in contact; for a given pair of surfaces, the coefficient of static friction is usually larger than that of kinetic friction; in some sets the two coefficients are equal, such as teflon-on-teflon.

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. Rubber in contact with other surfaces can yield friction coefficients from 1 to 2. Occasionally it is maintained that μ is always < 1, but this is not true. While in most relevant applications μ < 1, a value above 1 merely implies that the force required to slide an object along the surface is greater than the normal force of the surface on the object. For example, silicone rubber or acrylic rubber-coated surfaces have a coefficient of friction that can be substantially larger than 1.

While it is often stated that the COF is a "material property," it is better categorized as a "system property." Unlike true material properties (such as conductivity, dielectric constant, yield strength), the COF for any two materials depends on system variables like temperature, velocity, atmosphere and also what are now popularly described as aging and deaging times; as well as on geometric properties of the interface between the materials, namely surface structure. For example, a copper pin sliding against a thick copper plate can have a COF that varies from 0.6 at low speeds (metal sliding against metal) to below 0.2 at high speeds when the copper surface begins to melt due to frictional heating. The latter speed, of course, does not determine the COF uniquely; if the pin diameter is increased so that the frictional heating is removed rapidly, the temperature drops, the pin remains solid and the COF rises to that of a 'low speed' test.

In systems with significant non-uniform stress fields, because local slip occurs before the system slides, the macroscopic coefficient of static friction depends on the applied load, system size, or shape; Amontons' law is not satisfied macroscopically.

Approximate coefficients of friction
Under certain conditions some materials have very low friction coefficients. An example is (highly ordered pyrolytic) graphite which can have a friction coefficient below 0.01. This ultralow-friction regime is called superlubricity.

Static friction

Static friction is friction between two or more solid objects that are not moving relative to each other. For example, static friction can prevent an object from sliding down a sloped surface. The coefficient of static friction, typically denoted as μs, is usually higher than the coefficient of kinetic friction. Static friction is considered to arise as the result of surface roughness features across multiple length scales at solid surfaces. These features, known as asperities are present down to nano-scale dimensions and result in true solid to solid contact existing only at a limited number of points accounting for only a fraction of the apparent or nominal contact area. The linearity between applied load and true contact area, arising from asperity deformation, gives rise to the linearity between static frictional force and normal force, found for typical Amonton–Coulomb type friction.

The static friction force must be overcome by an applied force before an object can move. The maximum possible friction force between two surfaces before sliding begins is the product of the coefficient of static friction and the normal force: $$F_\text{max} = \mu_\mathrm{s} F_\text{n}$$. When there is no sliding occurring, the friction force can have any value from zero up to $$F_\text{max}$$. Any force smaller than $$F_\text{max}$$ attempting to slide one surface over the other is opposed by a frictional force of equal magnitude and opposite direction. Any force larger than $$F_\text{max}$$ overcomes the force of static friction and causes sliding to occur. The instant sliding occurs, static friction is no longer applicable—the friction between the two surfaces is then called kinetic friction. However, an apparent static friction can be observed even in the case when the true static friction is zero. An example of static friction is the force that prevents a car wheel from slipping as it rolls on the ground. Even though the wheel is in motion, the patch of the tire in contact with the ground is stationary relative to the ground, so it is static rather than kinetic friction. Upon slipping, the wheel friction changes to kinetic friction. An anti-lock braking system operates on the principle of allowing a locked wheel to resume rotating so that the car maintains static friction. The maximum value of static friction, when motion is impending, is sometimes referred to as limiting friction, although this term is not used universally.

Kinetic friction
Kinetic friction, also known as dynamic friction or sliding 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 for the same materials. However, Richard Feynman comments that "with dry metals it is very hard to show any difference." The friction force between two surfaces after sliding begins is the product of the coefficient of kinetic friction and the normal force: $$F_{k} = \mu_\mathrm{k} F_{n}$$. This is responsible for the Coulomb damping of an oscillating or vibrating system.

New models are beginning to show how kinetic friction can be greater than static friction. In many other cases roughness effects are dominant, for example in rubber to road friction. Surface roughness and contact area affect kinetic friction for micro- and nano-scale objects where surface area forces dominate inertial forces.

The origin of kinetic friction at nanoscale can be rationalized by an energy model. During sliding, a new surface forms at the back of a sliding true contact, and existing surface disappears at the front of it. Since all surfaces involve the thermodynamic surface energy, work must be spent in creating the new surface, and energy is released as heat in removing the surface. Thus, a force is required to move the back of the contact, and frictional heat is released at the front.

Angle of friction
For certain applications, it is more useful to define static friction in terms of the maximum angle before which one of the items will begin sliding. This is called the angle of friction or friction angle. It is defined as: $$\tan{\theta} = \mu_\mathrm{s}$$ and thus: $$\theta = \arctan{\mu_\mathrm{s}}$$ where $$\theta$$ is the angle from horizontal and μs is the static coefficient of friction between the objects. This formula can also be used to calculate μs from empirical measurements of the friction angle.

Friction at the atomic level
Determining the forces required to move atoms past each other is a challenge in designing nanomachines. In 2008 scientists for the first time were able to move a single atom across a surface, and measure the forces required. Using ultrahigh vacuum and nearly zero temperature (5 K), a modified atomic force microscope was used to drag a cobalt atom, and a carbon monoxide molecule, across surfaces of copper and platinum.

Limitations of the Coulomb model
The Coulomb approximation 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 the frictional force is proportional to the applied normal force, independently of the contact area. The Coulomb approximation is fundamentally an empirical construct. 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 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.

When the surfaces are conjoined, Coulomb friction becomes a very poor approximation (for example, adhesive 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 for this reason. However, despite the complexity of the fundamental physics behind friction, the relationships are accurate enough to be useful in many applications.

"Negative" coefficient of friction
, a single study has demonstrated the potential for an effectively negative coefficient of friction in the low-load regime, meaning that a decrease in normal force leads to an increase in friction. This contradicts everyday experience in which an increase in normal force leads to an increase in friction. This was reported in the journal Nature in October 2012 and involved the friction encountered by an atomic force microscope stylus when dragged across a graphene sheet in the presence of graphene-adsorbed oxygen.

Numerical simulation of the Coulomb model
Despite being a simplified model of friction, the Coulomb model is useful in many numerical simulation applications such as multibody systems and granular material. Even its most simple expression encapsulates the fundamental effects of sticking and sliding which are required in many applied cases, although specific algorithms have to be designed in order to efficiently numerically integrate mechanical systems with Coulomb friction and bilateral or unilateral contact. Some quite nonlinear effects, such as the so-called Painlevé paradoxes, may be encountered with Coulomb friction.

Dry friction and instabilities
Dry friction can induce several types of instabilities in mechanical systems which display a stable behaviour in the absence of friction. These instabilities may be caused by the decrease of the friction force with an increasing velocity of sliding, by material expansion due to heat generation during friction (the thermo-elastic instabilities), or by pure dynamic effects of sliding of two elastic materials (the Adams–Martins instabilities). The latter were originally discovered in 1995 by George G. Adams and João Arménio Correia Martins for smooth surfaces and were later found in periodic rough surfaces. In particular, friction-related dynamical instabilities are thought to be responsible for brake squeal and the 'song' of a glass harp, phenomena which involve stick and slip, modelled as a drop of friction coefficient with velocity.

A practically important case is the self-oscillation of the strings of bowed instruments such as the violin, cello, hurdy-gurdy, erhu, etc.

A connection between dry friction and flutter instability in a simple mechanical system has been discovered, watch the movie for more details.

Frictional instabilities can lead to the formation of new self-organized patterns (or "secondary structures") at the sliding interface, such as in-situ formed tribofilms which are utilized for the reduction of friction and wear in so-called self-lubricating materials.

Fluid friction
Fluid friction occurs between fluid layers that are moving relative to each other. This internal resistance to flow is named viscosity. In everyday terms, the viscosity of a fluid is described as its "thickness". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity. The less viscous the fluid, the greater its ease of deformation or movement.

All real fluids (except superfluids) offer some resistance to shearing and therefore are viscous. For teaching and explanatory purposes it is helpful to use the concept of an inviscid fluid or an ideal fluid which offers no resistance to shearing and so is not viscous.

Lubricated friction
Lubricated friction is a case of fluid friction where a fluid separates two solid surfaces. Lubrication is a technique employed to reduce wear of one or both surfaces in close proximity moving relative to each another by interposing a substance called a lubricant between the surfaces.

In most cases the applied load is carried by pressure generated within the fluid due to the frictional viscous resistance to motion of the lubricating fluid between the surfaces. Adequate lubrication allows smooth continuous operation of equipment, with only mild wear, and without excessive stresses or seizures at bearings. When lubrication breaks down, metal or other components can rub destructively over each other, causing heat and possibly damage or failure.

Skin friction
Skin friction arises from the interaction between the fluid and the skin of the body, and is directly related to the area of the surface of the body that is in contact with the fluid. Skin friction follows the drag equation and rises with the square of the velocity.

Skin friction is caused by viscous drag in the boundary layer around the object. There are two ways to decrease skin friction: the first is to shape the moving body so that smooth flow is possible, like an airfoil. The second method is to decrease the length and cross-section of the moving object as much as is practicable.

Internal friction
Internal friction is the force resisting motion between the elements making up a solid material while it undergoes deformation.

Plastic deformation in solids is an irreversible change in the internal molecular structure of an object. This change may be due to either (or both) an applied force or a change in temperature. The change of an object's shape is called strain. The force causing it is called stress.

Elastic deformation in solids is reversible change in the internal molecular structure of an object. Stress does not necessarily cause permanent change. As deformation occurs, internal forces oppose the applied force. If the applied stress is not too large these opposing forces may completely resist the applied force, allowing the object to assume a new equilibrium state and to return to its original shape when the force is removed. This is known as elastic deformation or elasticity.

Radiation friction
As a consequence of light pressure, Einstein in 1909 predicted the existence of "radiation friction" which would oppose the movement of matter. He wrote, "radiation will exert pressure on both sides of the plate. The forces of pressure exerted on the two sides are equal if the plate is at rest. However, if it is in motion, more radiation will be reflected on the surface that is ahead during the motion (front surface) than on the back surface. The backward-acting force of pressure exerted on the front surface is thus larger than the force of pressure acting on the back. Hence, as the resultant of the two forces, there remains a force that counteracts the motion of the plate and that increases with the velocity of the plate. We will call this resultant 'radiation friction' in brief."

Rolling resistance
Rolling resistance is the force that resists the rolling of a wheel or other circular object along a surface caused by deformations in the object or surface. Generally the force of rolling resistance is less than that associated with kinetic friction. Typical values for the coefficient of rolling resistance are 0.001. One of the most common examples of rolling resistance is the movement of motor vehicle tires on a road, a process which generates heat and sound as by-products.

Braking friction
Any wheel equipped with a brake is capable of generating a large retarding force, usually for the purpose of slowing and stopping a vehicle or piece of rotating machinery. Braking friction differs from rolling friction because the coefficient of friction for rolling friction is small whereas the coefficient of friction for braking friction is designed to be large by choice of materials for brake pads.

Triboelectric effect
Rubbing two materials against each other can lead to charge transfer, either electrons or ions. The energy required for this contributes to the friction. In addition, sliding can cause a build-up of electrostatic charge, which can be hazardous if flammable gases or vapours are present. When the static build-up discharges, explosions can be caused by ignition of the flammable mixture.

Belt friction
Belt friction is a physical property observed from the forces acting on a belt wrapped around a pulley, when one end is being pulled. The resulting tension, which acts on both ends of the belt, can be modeled by the belt friction equation.

In practice, the theoretical tension acting on the belt or rope calculated by the belt friction equation can be compared to the maximum tension the belt can support. This helps a designer of such a rig to know how many times the belt or rope must be wrapped around the pulley to prevent it from slipping. Mountain climbers and sailing crews demonstrate a standard knowledge of belt friction when accomplishing basic tasks.

Devices
Devices such as wheels, ball bearings, roller bearings, and air cushion or other types of fluid bearings can change sliding friction into a much smaller type of rolling friction.

Many thermoplastic materials such as nylon, HDPE and PTFE are commonly used in low friction bearings. They are especially useful because the coefficient of friction falls with increasing imposed load. For improved wear resistance, very high molecular weight grades are usually specified for heavy duty or critical bearings.

Lubricants
A common way to reduce friction is by using a lubricant, such as oil, water, or grease, 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.

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.

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.

Another way to reduce friction between two parts is to superimpose micro-scale vibration to one of the parts. This can be sinusoidal vibration as used in ultrasound-assisted cutting or vibration noise, known as dither.

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 thermal energy. A sliding hockey puck comes to rest because friction converts its kinetic energy into heat which raises the thermal energy of the puck and the ice surface. Since heat quickly dissipates, many early philosophers, including Aristotle, wrongly concluded that moving objects lose energy without a driving force.

When an object is pushed along a surface along a path C, the energy converted to heat is given by a line integral, in accordance with the definition of work
 * $$E_{th} = \int_C \mathbf{F}_\mathrm{fric}(\mathbf{x}) \cdot d\mathbf{x}\ = \int_C \mu_\mathrm{k}\ \mathbf{F}_\mathrm{n}(\mathbf{x}) \cdot d\mathbf{x}, $$

where
 * $$\mathbf{F}_\mathrm{fric}$$ is the friction force,
 * $$\mathbf{F}_\mathrm{n}$$ is the vector obtained by multiplying the magnitude of the normal force by a unit vector pointing against the object's motion,
 * $$\mu_\mathrm{k}$$ is the coefficient of kinetic friction, which is inside the integral because it may vary from location to location (e.g. if the material changes along the path),
 * $$\mathbf{x}$$ is the position of the object.

Dissipation of energy by friction in a process is a classic example of thermodynamic irreversibility.

Work of friction
The work done by friction can translate into deformation, wear, and heat that can affect the contact surface properties (even the coefficient of friction between the surfaces). This can be beneficial as in polishing. The work of friction is used to mix and join materials such as in the process of friction welding. Excessive erosion or wear of mating sliding surfaces occurs when work due to frictional forces rise to unacceptable levels. Harder corrosion particles caught between mating surfaces in relative motion (fretting) exacerbates wear of frictional forces. As surfaces are worn by work due to friction, fit and surface finish of an object may degrade until it no longer functions properly. For example, bearing seizure or failure may result from excessive wear due to work of friction.

In the reference frame of the interface between two surfaces, static friction does no work, because there is never displacement between the surfaces. In the same reference frame, kinetic friction is always in the direction opposite the motion, and does negative work. However, friction can do positive work in certain frames of reference. 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 frame of reference in which the floor is stationary. Thus, the kinetic friction between the box and rug accelerates the box in the same direction that the box moves, doing positive work.

When sliding takes place between two rough bodies in contact, the algebraic sum of the works done is different from zero, and the algebraic sum of the quantities of heat gained by the two bodies is equal to the quantity of work lost by friction, and the total quantity of heat gained is positive. In a natural thermodynamic process, the work done by an agency in the surroundings of a thermodynamic system or working body is greater than the work received by the body, because of friction. Thermodynamic work is measured by changes in a body's state variables, sometimes called work-like variables, other than temperature and entropy. Examples of work-like variables, which are ordinary macroscopic physical variables and which occur in conjugate pairs, are pressure – volume, and electric field – electric polarization. Temperature and entropy are a specifically thermodynamic conjugate pair of state variables. They can be affected microscopically at an atomic level, by mechanisms such as friction, thermal conduction, and radiation. The part of the work done by an agency in the surroundings that does not change the volume of the working body but is dissipated in friction, is called isochoric work. It is received as heat, by the working body and sometimes partly by a body in the surroundings. It is not counted as thermodynamic work received by the working body.

Applications
Friction is an important factor in many engineering disciplines.

Transportation

 * Automobile brakes inherently rely on friction, slowing a vehicle by converting its kinetic energy into heat. Incidentally, dispersing this large amount of heat safely is one technical challenge in designing brake systems. Disk brakes rely on friction between a disc and brake pads that are squeezed transversely against the rotating disc. In drum brakes, brake shoes or pads are pressed outwards against a rotating cylinder (brake drum) to create friction. Since braking discs can be more efficiently cooled than drums, disc brakes have better stopping performance.
 * Rail adhesion refers to the grip wheels of a train have on the rails, see Frictional contact mechanics.
 * Road slipperiness is an important design and safety factor for automobiles
 * Split friction is a particularly dangerous condition arising due to varying friction on either side of a car.
 * Road texture affects the interaction of tires and the driving surface.

Measurement

 * A tribometer is an instrument that measures friction on a surface.
 * A profilograph is a device used to measure pavement surface roughness.

Household usage

 * Friction is used to heat and ignite matchsticks (friction between the head of a matchstick and the rubbing surface of the match box).
 * Sticky pads are used to prevent object from slipping off smooth surfaces by effectively increasing the friction coefficient between the surface and the object.

title: Friction


text:
February 7

Pre-1600

 * 457 – Leo I becomes the Eastern Roman emperor.
 * 987 – Bardas Phokas the Younger and Bardas Skleros, Byzantine generals of the military elite, begin a wide-scale rebellion against Emperor Basil II.
 * 1301 – Edward of Caernarvon (later king Edward II of England) becomes the first English Prince of Wales.
 * 1313 – King Thihathu founds the Pinya Kingdom as the de jure successor state of the Pagan Kingdom.
 * 1365 – Albert III of Mecklenburg (King Albert of Sweden) grants city rights to Ulvila (Ulvsby).
 * 1497 – In Florence, Italy, supporters of Girolamo Savonarola burn cosmetics, art, and books, in a "Bonfire of the vanities".

1601–1900

 * 1756 – Guaraní War: The leader of the Guaraní rebels, Sepé Tiaraju, is killed in a skirmish with Spanish and Portuguese troops.
 * 1783 – American Revolutionary War: French and Spanish forces lift the Great Siege of Gibraltar.
 * 1795 – The 11th Amendment to the United States Constitution is ratified.
 * 1807 – Napoleonic Wars: Napoleon finds Bennigsen's Russian forces taking a stand at Eylau. After bitter fighting, the French take the town, but the Russians resume the battle the next day.
 * 1812 – The strongest in a series of earthquakes strikes New Madrid, Missouri.
 * 1813 – In the action of 7 February 1813 near the Îles de Los, the frigates Aréthuse and Amelia batter each other, but neither can gain the upper hand.
 * 1819 – Sir Thomas Stamford Raffles leaves Singapore after just taking it over, leaving it in the hands of William Farquhar.
 * 1842 – Battle of Debre Tabor: Ras Ali Alula, Regent of the Emperor of Ethiopia defeats warlord Wube Haile Maryam of Semien.
 * 1854 – A law is approved to found the Swiss Federal Institute of Technology. Lectures started October 16, 1855.
 * 1863 – HMS Orpheus (1860) sinks off the coast of Auckland, New Zealand, killing 189.
 * 1894 – The Cripple Creek miner's strike, led by the Western Federation of Miners, begins in Cripple Creek, Colorado, United States.
 * 1898 – Dreyfus affair: Émile Zola is brought to trial for libel for publishing J'Accuse...!
 * 1900 – Second Boer War: British troops fail in their third attempt to lift the Siege of Ladysmith.
 * 1900  – A Chinese immigrant in San Francisco falls ill to bubonic plague in the first plague epidemic in the continental United States.

1901–present

 * 1904 – The Great Baltimore Fire begins in Baltimore, Maryland; it destroys over 1,500 buildings in 30 hours.
 * 1940 – The second full-length animated Walt Disney film, Pinocchio, premieres.
 * 1943 – World War II: Imperial Japanese Navy forces complete the evacuation of Imperial Japanese Army troops from Guadalcanal during Operation Ke, ending Japanese attempts to retake the island from Allied forces in the Guadalcanal Campaign.
 * 1944 – World War II: In Anzio, Italy, German forces launch a counteroffensive during the Allied Operation Shingle.
 * 1951 – Korean War: More than 700 suspected communist sympathizers are massacred by South Korean forces.
 * 1962 – The United States bans all Cuban imports and exports.
 * 1964 – The Beatles land in the United States for the first time, at the newly renamed John F. Kennedy International Airport.
 * 1966 – The Great Fire of Iloilo breaks out in a lumber yard in Iznart Street and burns for almost half a day destroying nearly three-quarters of the City Proper area and Php 50 million pesos in total properties' damage.
 * 1974 – Grenada gains independence from the United Kingdom.
 * 1979 – Pluto moves inside Neptune's orbit for the first time since either was discovered.
 * 1981 – A plane crash at Pushkin Airport kills 50 people, including 16 members of the Pacific Fleet.
 * 1984 – Space Shuttle program: STS-41-B Mission: astronauts Bruce McCandless II and Robert L. Stewart make the first untethered space walk using the Manned Maneuvering Unit (MMU).
 * 1986 – Twenty-eight years of one-family rule end in Haiti, when President Jean-Claude Duvalier flees the Caribbean nation.
 * 1990 – Dissolution of the Soviet Union: The Central Committee of the Soviet Communist Party agrees to give up its monopoly on power.
 * 1991 – Haiti's first democratically elected president, Jean-Bertrand Aristide, is sworn in.
 * 1991  – The Troubles: The Provisional IRA launches a mortar attack on 10 Downing Street in London, the headquarters of the British government.
 * 1992 – The Maastricht Treaty is signed, leading to the creation of the European Union.
 * 1995 – Ramzi Yousef, the mastermind of the 1993 World Trade Center bombing, is arrested in Islamabad, Pakistan.
 * 1999 – Crown Prince Abdullah becomes the King of Jordan on the death of his father, King Hussein.
 * 2001 – Space Shuttle program: Space Shuttle Atlantis is launched on mission STS-98, carrying the Destiny laboratory module to the International Space Station.
 * 2009 – Bushfires in Victoria leave 173 dead in the worst natural disaster in Australia's history.
 * 2012 – President Mohamed Nasheed of the Republic of Maldives resigns, after 23 days of anti-governmental protests calling for the release of the Chief Judge unlawfully arrested by the military.
 * 2013 – The U.S. state of Mississippi officially certifies the Thirteenth Amendment, becoming the last state to approve the abolition of slavery. The Thirteenth Amendment was formally ratified by Mississippi in 1995.
 * 2014 – Scientists announce that the Happisburgh footprints in Norfolk, England, date back to more than 800,000 years ago, making them the oldest known hominid footprints outside Africa.
 * 2016 – North Korea launches Kwangmyŏngsŏng-4 into outer space violating multiple UN treaties and prompting condemnation from around the world.
 * 2021 – The 2021 Uttarakhand flood begins.
 * 2024 - Pakistan election offices hit by twin bombings, killing at least 24 people a day before general elections.

Pre-1600

 * 574 – Prince Shōtoku of Japan (d. 622)
 * 1102 – Empress Matilda, Holy Roman Empress and claimant to the English throne (probable; d. 1167)
 * 1449 – Adriana of Nassau-Siegen, German countess (d. 1477)
 * 1478 – Thomas More, English lawyer and politician, Lord Chancellor of England (d. 1535)
 * 1487 – Queen Dangyeong, Korean royal consort (d. 1557)
 * 1500 – João de Castro, viceroy of Portuguese India (d. 1548)

1601–1900

 * 1612 – Thomas Killigrew, English playwright and manager (d. 1683)
 * 1622 – Vittoria della Rovere, Italian noble (d. 1694)
 * 1693 – Empress Anna of Russia (d. 1740)
 * 1722 – Azar Bigdeli, Iranian anthologist and poet (d. 1781)
 * 1726 – Margaret Fownes-Luttrell, English painter (d. 1766)
 * 1741 – Henry Fuseli, Swiss-English painter and academic (d. 1825)
 * 1758 – Benedikt Schack, Czech tenor and composer (d. 1826)
 * 1796 – Thomas Gregson, English-Australian lawyer and politician, 2nd Premier of Tasmania (baptism date; d. 1874)
 * 1802 – Louisa Jane Hall, American poet, essayist, and literary critic (d. 1892)
 * 1804 – John Deere, American blacksmith and businessman, founded Deere & Company (d. 1886)
 * 1812 – Charles Dickens, English novelist and critic (d. 1870)
 * 1825 – Karl Möbius, German zoologist and ecologist (d. 1908)
 * 1834 – Alfred-Philibert Aldrophe, French architect (d. 1895)
 * 1837 – James Murray, Scottish lexicographer and philologist (d. 1915)
 * 1864 – Arthur Collins, American baritone singer (d. 1933)
 * 1867 – Laura Ingalls Wilder, American author (d. 1957)
 * 1870 – Alfred Adler, Austrian-Scottish psychologist and therapist (d. 1937)
 * 1871 – Wilhelm Stenhammar, Swedish pianist, composer, and conductor (d. 1927)
 * 1873 – Thomas Andrews, Irish shipbuilder and businessman, designed the RMS Titanic (d. 1912)
 * 1875 – Erkki Melartin, Finnish composer (d. 1937)
 * 1877 – G. H. Hardy, English mathematician and geneticist (d. 1947)
 * 1878 – Ossip Gabrilowitsch, Russian-American pianist and conductor (d. 1936)
 * 1885 – Sinclair Lewis, American novelist, short-story writer, and playwright, Nobel Prize laureate (d. 1951)
 * 1885  – Hugo Sperrle, German field marshal (d. 1953)
 * 1887 – Eubie Blake, American pianist and composer (d. 1983)
 * 1889 – Harry Nyquist, Swedish-American engineer and theorist (d. 1976)
 * 1893 – Joseph Algernon Pearce, Canadian astrophysicist and astronomer (d. 1988)
 * 1893  – Nicanor Abelardo, Filipino pianist, composer and teacher (d. 1934)
 * 1895 – Anita Stewart, American actress (d. 1961)

1901–present

 * 1901 – Arnold Nordmeyer, New Zealand minister and politician, 30th New Zealand Minister of Finance (d. 1989)
 * 1904 – Ernest E. Debs, American politician (d. 2002)
 * 1905 – Paul Nizan, French philosopher and author (d. 1940)
 * 1905  – Ulf von Euler, Swedish physiologist and academic, Nobel Prize laureate (d. 1983)
 * 1906 – Oleg Antonov, Soviet engineer, founded the Antonov Design Bureau (d. 1984)
 * 1906  – Puyi, Chinese emperor (d. 1967)
 * 1908 – Buster Crabbe, American swimmer and actor (d. 1983)
 * 1908  – Manmath Nath Gupta, Indian journalist and author (d. 2000)
 * 1909 – Hélder Câmara, Brazilian archbishop (d. 1999)
 * 1909  – Amedeo Guillet, Italian soldier (d. 2010)
 * 1912 – Russell Drysdale, English-Australian painter (d. 1981)
 * 1912  – Roberta McCain, American socialite and oil heiress (d. 2020)
 * 1915 – Teoctist Arăpașu, Romanian patriarch (d. 2007)
 * 1915  – Eddie Bracken, American actor and singer (d. 2002)
 * 1916 – Frank Hyde, Australian rugby league player, coach, and sportscaster (d. 2007)
 * 1919 – Desmond Doss, American army corporal and combat medic, Medal of Honor recipient (d. 2006)
 * 1919  – Jock Mahoney, American actor and stuntman (d. 1989)
 * 1920 – Oscar Brand, Canadian-American singer-songwriter and author (d. 2016)
 * 1920  – An Wang, Chinese-American engineer and businessman, founded Wang Laboratories (d. 1990)
 * 1921 – Athol Rowan, South African cricketer (d. 1998)
 * 1922 – Hattie Jacques, English actress (d. 1980)
 * 1923 – Dora Bryan, English actress and restaurateur (d. 2014)
 * 1925 – Hans Schmidt, Canadian wrestler (d. 2012)
 * 1926 – Konstantin Feoktistov, Russian engineer and astronaut (d. 2009)
 * 1927 – Juliette Gréco, French singer and actress (d. 2020)
 * 1927  – Vladimir Kuts, Ukrainian-Russian runner and coach (d. 1975)
 * 1927  – Lalo Ríos, Mexican actor (d. 1973)
 * 1928 – Lincoln D. Faurer, American general (d. 2014)
 * 1929 – Jim Langley, English international footballer and manager (d. 2007)
 * 1932 – Gay Talese, American journalist and memoirist
 * 1932  – Alfred Worden, American colonel, pilot, and astronaut (d. 2020)
 * 1933 – K. N. Choksy, Sri Lankan lawyer and politician, Sri Lankan Minister of Finance (d. 2015)
 * 1934 – Eddie Fenech Adami, Maltese lawyer and politician, 7th President of Malta
 * 1934  – King Curtis, American saxophonist and producer (d. 1971)
 * 1934  – Earl King, American singer-songwriter, guitarist, and producer (d. 2003)
 * 1935 – Cliff Jones, Welsh international footballer
 * 1935  – Herb Kohl, American businessman and politician (d. 2023)
 * 1935  – Jörg Schneider, Swiss actor and author (d. 2015)
 * 1936 – Jas Gawronski, Italian journalist and politician
 * 1937 – Peter Jay, English economist, journalist, and diplomat, British Ambassador to the United States
 * 1937  – Juan Pizarro, Puerto Rican baseball player (d. 2021)
 * 1940 – Tony Tan, Singaporean academic and politician, 7th President of Singapore
 * 1942 – Gareth Hunt, English actor (d. 2007)
 * 1943 – Eric Foner, American historian, author, and academic
 * 1945 – Gerald Davies, Welsh rugby player and journalist
 * 1946 – Héctor Babenco, Argentinian-Brazilian director, producer, and screenwriter (d. 2016)
 * 1946  – Gérard Jean-Juste, Haitian priest and activist (d. 2009)
 * 1946  – Pete Postlethwaite, English actor (d. 2011)
 * 1949 – Jacques Duchesneau, Canadian police officer and politician
 * 1949 – Alan Lancaster, English Australian bass player singer and songwriter Status Quo (d. 2022)
 * 1950 – Karen Joy Fowler, American author
 * 1953 – Robert Brazile, American football player
 * 1954 – Dieter Bohlen, German singer-songwriter and producer
 * 1955 – Rolf Benirschke, American football player and game show host
 * 1955  – Miguel Ferrer, American actor and director (d. 2017)
 * 1956 – John Nielsen, Danish racing driver
 * 1956  – Mark St. John, American guitarist (d. 2007)
 * 1957 – Dámaso García, Dominican baseball player and footballer (d. 2020)
 * 1958 – Giuseppe Baresi, Italian footballer and manager
 * 1958  – Terry Marsh, English boxer and politician
 * 1958  – Matt Ridley, English journalist, author, and politician
 * 1959 – Mick McCarthy, English footballer, manager, and sportscaster
 * 1960 – Robert Smigel, American actor, producer, and screenwriter
 * 1960  – James Spader, American actor and producer
 * 1962 – Garth Brooks, American singer-songwriter and guitarist
 * 1962  – David Bryan, American keyboard player and songwriter
 * 1962  – Eddie Izzard, English comedian, actor, and producer
 * 1963 – Heidemarie Stefanyshyn-Piper, American Naval officer and astronaut
 * 1964 – Ashok Banker, Indian journalist, author, and screenwriter
 * 1965 – Chris Rock, American actor, director, producer, and screenwriter
 * 1966 – Kristin Otto, German swimmer
 * 1968 – Peter Bondra, Ukrainian-Slovak ice hockey player and manager
 * 1968  – Sully Erna, American singer-songwriter and musician
 * 1968  – Mark Tewksbury, Canadian swimmer and sportscaster
 * 1969 – Andrew Micallef, Maltese painter and musician
 * 1971 – Anita Tsoy, Russian singer-songwriter
 * 1972 – Essence Atkins, American actress
 * 1972  – Robyn Lively, American actress
 * 1973 – Juwan Howard, American basketball player and coach
 * 1974 – J Dilla, American rapper and producer (d. 2006)
 * 1974  – Steve Nash, South African-Canadian basketball player
 * 1974  – Nujabes, Japanese record producer, DJ, composer and arranger (d. 2010)
 * 1975 – Wes Borland, American singer-songwriter and guitarist
 * 1975  – Miriam Corowa, Australian journalist, television presenter and producer
 * 1975  – Alexandre Daigle, Canadian ice hockey player
 * 1975  – Rémi Gaillard, French comedian and actor
 * 1976 – Chito Miranda, Filipino singer-songwriter
 * 1977 – Tsuneyasu Miyamoto, Japanese footballer
 * 1978 – David Aebischer, Swiss ice hockey player
 * 1978  – Endy Chávez, Venezuelan baseball player
 * 1978  – Ashton Kutcher, American model, actor, producer, and entrepreneur
 * 1978  – Milt Palacio, American-Belizean basketball player and coach
 * 1978  – Daniel Van Buyten, Belgian footballer
 * 1979 – Daniel Bierofka, German footballer and coach
 * 1979  – Tawakkol Karman, Yemeni journalist and activist, Nobel Prize laureate
 * 1979  – Sam J. Miller, American author
 * 1980 – Dalibor Bagarić, Croatian basketball player
 * 1981 – Neto, Brazilian footballer
 * 1981  – Lee Ok-sung, South Korean boxer
 * 1982 – Mohammed Bijeh, Iranian serial killer (d. 2006)
 * 1982  – Osamu Mukai, Japanese actor
 * 1982  – Mickaël Piétrus, French basketball player
 * 1983 – Scott Feldman, American baseball player
 * 1983  – Sho Kamogawa, Japanese footballer
 * 1983  – Federico Marchetti, Italian footballer
 * 1984 – Trey Hardee, American decathlete
 * 1984  – Jeremy Meeks American model and actor
 * 1985 – Josh Hennessy, American ice hockey player
 * 1985  – Bernard James, American basketball player
 * 1985  – Tina Majorino, American actress
 * 1985  – Deborah Ann Woll, American actress
 * 1987 – Joel Freeland, English basketball player
 * 1988 – Ai Kago, Japanese singer and actress
 * 1988  – Matthew Stafford, American football player
 * 1989 – Nick Calathes, American-Greek basketball player
 * 1989  – Isaiah Thomas, American basketball player
 * 1989  – Elia Viviani, Italian cyclist
 * 1990 – Morris Claiborne, American football player
 * 1990  – Jacksepticeye, Irish YouTuber
 * 1990  – Gianluca Lapadula, Italian footballer
 * 1990  – Dalilah Muhammad, American hurdler
 * 1990  – Steven Stamkos, Canadian ice hockey player
 * 1991 – Gabbie Hanna, American Internet personality and singer-songwriter
 * 1991  – Ryan O'Reilly, Canadian ice hockey player
 * 1991  – Richard Pánik, Slovak ice hockey player
 * 1992 – Sergi Roberto, Spanish footballer
 * 1992  – Ksenia Stolbova, Russian figure skater
 * 1992  – Maimi Yajima, Japanese singer and actress
 * 1993 – Javon Hargrave, American football player
 * 1993  – Chris Mears, English diver
 * 1994 – Riley Barber, American ice hockey player
 * 1994  – Nathan Walker, Welsh-Australian ice hockey player
 * 1995 – Tom Glynn-Carney, English actor and musician
 * 1995  – Roberto Osuna, Mexican baseball player
 * 1996 – Aaron Ekblad, Canadian ice hockey player
 * 1996  – Pierre Gasly, French racing driver
 * 1997 – Nicolò Barella, Italian footballer
 * 1997  – Anhelina Kalinina, Ukrainian tennis player
 * 1999 – Omar Marmoush, Egyptian footballer
 * 2001 – R. J. Hampton, American basketball player
 * 2003 – Alessandro Fontanarosa, Italian footballer

Pre-1600

 * 199 – Lü Bu, Chinese warlord
 * 318 – Jin Mindi, emperor of the Jin Dynasty (b. 300)
 * 999 – Boleslaus II the Pious, Duke of Bohemia (b. 932)
 * 1045 – Emperor Go-Suzaku of Japan (b. 1009)
 * 1065 – Siegfried I, Count of Sponheim (b. c. 1010)
 * 1127 – Ava, German poet (b. 1060)
 * 1165 – Marshal Stephen of Armenia
 * 1259 – Thomas, Count of Flanders
 * 1317 – Robert, Count of Clermont (b. 1256)
 * 1320 – Jan Muskata, Bishop of Kraków (b. 1250)
 * 1333 – Nikko, Japanese priest, founder of Nichiren Shoshu Buddhism (b. 1246)
 * 1520 – Alfonsina de' Medici, Regent of Florence (b. 1472)
 * 1560 – Bartolommeo Bandinelli, Florentine sculptor (b. 1493)

1601–1900

 * 1603 – Bartholomäus Sastrow, German politician (b. 1520)
 * 1623 – Thomas Cecil, 1st Earl of Exeter, English soldier and politician, Lord Lieutenant of Northamptonshire (b. 1546)
 * 1626 – William V, Duke of Bavaria (b. 1548)
 * 1642 – William Bedell, English bishop and academic (b. 1571)
 * 1693 – Paul Pellisson, French lawyer and author (b. 1624)
 * 1736 – Stephen Gray, English astronomer and physicist (b. 1666)
 * 1779 – William Boyce, English organist and composer (b. 1711)
 * 1799 – Qianlong Emperor of China (b. 1711)
 * 1801 – Daniel Chodowiecki, Polish-German painter and academic (b. 1726)
 * 1819 – August Wilhelm Hupel, German-Estonian linguist and author (b. 1737)
 * 1823 – Ann Radcliffe, English author (b. 1764)
 * 1837 – Gustav IV Adolf of Sweden (b. 1778)
 * 1849 – Mariano Paredes, Mexican general and 16th president (1845-1846) (b. 1797)
 * 1862 – Francisco de Paula Martínez de la Rosa y Berdejo, Spanish playwright and politician, Prime Minister of Spain (b. 1787)
 * 1864 – Vuk Karadžić, Serbian philologist and linguist (b. 1787)
 * 1871 – Henry E. Steinway, German-American businessman, founded Steinway & Sons (b. 1797)
 * 1873 – Sheridan Le Fanu, Irish author (b. 1814)
 * 1878 – Pope Pius IX (b. 1792)
 * 1891 – Marie Louise Andrews, American story writer and journalist (b. 1849)
 * 1897 – Galileo Ferraris, Italian physicist and engineer (b. 1847)

1901–present

 * 1919 – William Halford, English-American lieutenant, Medal of Honor recipient (b. 1841)
 * 1920 – Alexander Kolchak, Russian admiral and explorer (b. 1874)
 * 1920  – Charles Langelier, Canadian journalist, judge, and politician (b. 1850)
 * 1921 – John J. Gardner, American politician (b. 1845)
 * 1937 – Elihu Root, American lawyer and politician, 38th United States Secretary of State, Nobel Prize laureate (b. 1845)
 * 1938 – Harvey Samuel Firestone, American businessman, founded the Firestone Tire and Rubber Company (b. 1868)
 * 1939 – Boris Grigoriev, Russian painter and illustrator (b. 1886)
 * 1940 – James McCormick (Irish republican), Executed Irish Republican (b. 1910)
 * 1940  – Peter Barnes (Irish republican), Executed Irish Republican (b. 1907)
 * 1942 – Ivan Bilibin, Russian illustrator and stage designer (b. 1876)
 * 1944 – Lina Cavalieri, Italian soprano and actress (b. 1874)
 * 1959 – Nap Lajoie, American baseball player and manager (b. 1874)
 * 1959  – Daniel François Malan, South African minister and politician, 5th Prime Minister of South Africa (b. 1874)
 * 1959  – Guitar Slim, American singer and guitarist (b. 1926)
 * 1960 – Igor Kurchatov, Russian physicist and academic (b. 1903)
 * 1963 – Learco Guerra, Italian cyclist and manager (b. 1902)
 * 1964 – Sofoklis Venizelos, Greek captain and politician, 133rd Prime Minister of Greece (b. 1894)
 * 1968 – Nick Adams, American actor and screenwriter (b. 1931)
 * 1972 – Walter Lang, American director and screenwriter (b. 1896)
 * 1979 – Josef Mengele, German SS officer and physician (b. 1911)
 * 1986 – Cheikh Anta Diop, Senegalese historian, anthropologist, and physicist (b. 1923)
 * 1990 – Alan Perlis, American computer scientist and academic (b. 1922)
 * 1990  – Alfredo M. Santos, Filipino general (b. 1905)
 * 1991 – Amos Yarkoni, Israeli colonel (b. 1920)
 * 1994 – Witold Lutosławski, Polish composer and conductor (b. 1913)
 * 1999 – King Hussein of Jordan (b. 1935)
 * 1999  – Bobby Troup, American actor, pianist, and composer (b. 1918)
 * 2000 – Doug Henning, Canadian magician and politician (b. 1947)
 * 2001 – Anne Morrow Lindbergh, American author and pilot (b. 1906)
 * 2003 – Augusto Monterroso, Guatemalan author (b. 1921)
 * 2005 – Atli Dam, Faroese engineer and politician, 5th Prime Minister of the Faroe Islands (b. 1932)
 * 2006 – Princess Durru Shehvar of the Ottoman Empire (b. 1914)
 * 2009 – Blossom Dearie, American singer and pianist (b. 1924)
 * 2010 – Franco Ballerini, Italian cyclist and coach (b. 1964)
 * 2012 – Harry Keough, American soccer player and coach (b. 1927)
 * 2013 – Krsto Papić, Croatian director and screenwriter (b. 1933)
 * 2014 – Doug Mohns, Canadian-American ice hockey player (b. 1933)
 * 2015 – Billy Casper, American golfer (b. 1931)
 * 2015  – Marshall Rosenberg, American psychologist and author (b. 1934)
 * 2015  – Dean Smith, American basketball player and coach (b. 1931)
 * 2015  – John C. Whitehead, American banker and politician, 9th United States Deputy Secretary of State (b. 1922)
 * 2017 – Richard Hatch, American actor (b. 1945)
 * 2017  – Hans Rosling, Swedish academic (b. 1948)
 * 2017  – Tzvetan Todorov, Bulgarian philosopher (b. 1939)
 * 2019 – John Dingell, American politician (b. 1926)
 * 2019  – Albert Finney, English actor (b. 1936)
 * 2019  – Jan Olszewski, Polish politician, 3rd Prime Minister (b. 1930)
 * 2019  – Frank Robinson, American baseball player, coach, and manager (b. 1935)
 * 2020 – Li Wenliang, Chinese ophthalmologist who initially warned about COVID-19 (b. 1986)

Holidays and observances

 * Christian feast day:
 * Richard the Pilgrim
 * Blessed Eugénie Smet
 * Blessed Pope Pius IX
 * Chrysolius
 * Egidio Maria of Saint Joseph
 * February 7 (Eastern Orthodox liturgics)
 * New Martyrs and Confessors of the Russian Orthodox Church Typically observed on the Sunday closest to January 25 (O.S.)/February 7 (N.S.)
 * Independence Day (Grenada), celebrates the independence of Grenada from the United Kingdom in 1974.
 * National Black HIV/AIDS Awareness Day (United States)

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: February 7


text:
Faith

Faith is confidence or trust in a person, thing, or concept. In the context of religion, faith is "belief in God or in the doctrines or teachings of religion". According to the Merriam-Webster's Dictionary, faith has multiple definitions, including "something that is believed especially with strong conviction", "complete trust", "belief and trust in and loyalty to God", as well as "a firm belief in something for which there is no proof".

Religious people often think of faith as confidence based on a perceived degree of warrant, or evidence, while others who are more skeptical of religion tend to think of faith as simply belief without evidence.

In the Roman world, 'faith' (Latin: fides) was understood without particular association with gods or beliefs. Instead, it was understood as a paradoxical set of reciprocal ideas: voluntary will and voluntary restraint in the sense of father over family or host over guest, whereby one party willfully surrenders to a party who could harm but chooses not to, thereby entrusting or confiding in them.

Accordingly to Thomas Aquinas, faith is "an act of the intellect assenting to the truth at the command of the will".

Religion has a long tradition, since the ancient world, of analyzing divine questions using common human experiences such as sensation, reason, science, and history that do not rely on revelation—called Natural theology.

Etymology
The English word faith finds its roots in the Proto-Indo-European (PIE) root *bheidh-, signifying concepts of trust, confidence, and persuasion. This root has given rise to various terms across different languages, such as Greek πίστις (pístis), meaning "faith", and Latin fidēs, meaning "trust", "faith", "confidence".

Furthermore, the Proto-Indo-European root *were-o- adds another layer to the word's etymology, emphasizing the notions of truth and trustworthiness. This root is evident in English words like veracity, verity, and verify, as well as in Latin with verus, meaning "true".

The term faith in English emerged in the mid-13th century, evolving from Anglo-French and Old French forms like feid and feit, ultimately tracing back to the Latin fidēs. This Latin term, rooted in the PIE root *bheidh-, encompassed meanings such as trust, confidence, and belief.

Stages of faith development
James W. Fowler (1940–2015) proposes a series of stages of faith development (or spiritual development) across the human lifespan. His stages relate closely to the work of Piaget, Erikson, and Kohlberg regarding aspects of psychological development in children and adults. Fowler defines faith as an activity of trusting, committing, and relating to the world based on a set of assumptions of how one is related to others and the world.

 * Stages of faith:
 * 1) Intuitive-Projective: confusion and of high impressionability through stories and rituals (pre-school period).
 * 2) Mythic-Literal: provided information is accepted to conform with social norms (school-going period).
 * 3) Synthetic-Conventional: the faith acquired is concreted in the belief system with the forgoing of personification and replacement with authority in people or groups that represent one's beliefs (early late adolescence).
 * 4) Individuative-Reflective: the person critically analyzes adopted and accepted faith with existing systems of faith. Disillusion or strengthening of faith happens in this stage. Based on needs, experiences, and paradoxes (early adulthood).
 * 5) Conjunctive faith: people realize the limits of logic and, facing the paradoxes or transcendence of life, accept the "mystery of life" and often return to the sacred stories and symbols of the pre-acquired or re-adopted faith system. This stage is called negotiated settling in life (mid-life).
 * 6) Universalizing faith: this is the "enlightenment" stage where the person comes out of all the existing systems of faith and lives life with universal principles of compassion and love and in service to others for uplift, without worries and doubt (middle-late adulthood, 45–65 years old and beyond).

No hard-and-fast rule requires that people pursue faith by going through all six stages. There is a high probability for people to be content and fixed in a particular stage for a lifetime; stages 2–5 are such stages. Stage 6 is the summit of faith development. This state is often considered as "not fully" attainable.

Extent of religious faith
Referring to "religions" (plural), Pope Francis claims that "the majority of people living on our planet profess to be believers".

Christianity

The word translated as "faith" in English-language editions of the New Testament, the Greek word πίστις, can also be translated as "belief", "faithfulness", or "trust". Faith can also be translated from the Greek verb πιστεύω, meaning "to trust, to have confidence, faithfulness, to be reliable, to assure". Christianity encompasses various views regarding the nature of faith. Some see faith as being persuaded or convinced that something is true. In this view, a person believes something when they are presented with adequate evidence that it is true. The 13th-century theologian Saint Thomas Aquinas did not hold that faith is mere opinion: on the contrary, he held that it represents a mean (understood in the Aristotelian sense) between excessive reliance on science (i.e. demonstration) and excessive reliance on opinion.

According to Teresa Morgan, faith was understood by early Christians within the cultural milieu of the period as a relationship that created a community based on trust, instead of a set of mental beliefs or feelings of the heart.

Numerous commentators discuss the results of faith. Some believe that true faith results in good works, while others believe that while faith in Jesus brings eternal life, it does not necessarily result in good works.

Regardless of the approach taken to faith, all Christians agree that the Christian faith (in the sense of Christian practice) is aligned with the ideals and the example of the life of Jesus. The Christian contemplates the mystery of God and his grace and seeks to know and become obedient to God. To a Christian, the faith is not static, but causes one to learn more of God and to grow in faith; Christian faith has its origin in God.

In Christianity, faith causes change as it seeks a greater understanding of God. Faith is not fideism or simple obedience to a set of rules or statements. Before Christians have faith, but they must also understand in whom and in what they have faith. Without understanding, there cannot be true faith, and that understanding is built on the foundation of the community of believers, the scriptures and traditions, and on the personal experiences of the believer.

Strength of faith
Christians may recognize different degrees of faith when they encourage each other to, and themselves strive to, develop, grow, and/or deepen their faith. This may imply that one can measure faith. Willingness to undergo martyrdom indicates a proxy for depth of faith but does not provide an everyday measurement for the average contemporary Christian. Within the Calvinist tradition the degree of prosperity may serve as an analog of the level of faith. Other Christian strands may rely on personal self-evaluation to measure the intensity of an individual's faith, with associated difficulties in calibrating to any scale. Solemn affirmations of a creed (a statement of faith) provide Various tribunals of the Inquisition, however, concerned themselves with precisely evaluating the orthodoxy of the faith of those it examined – to acquit or to punish in varying degrees.

The classification of different degrees of faith allows that faith and its expression may wax and wane in fervor—during the lifetime of a faithful individual and/or over the various historical centuries of a society with an embedded religious system. Thus, one can speak of an "Age of Faith" or of the "decay" of a society's religiosity into corruption, secularism, or atheism, —interpretable as the ultimate loss of faith.

Christian apologetic views
In contrast to Richard Dawkins' view of faith as "blind trust, in the absence of evidence, even in the teeth of evidence", Alister McGrath quotes the Oxford Anglican theologian W. H. Griffith Thomas (1861–1924), who states that faith is "not blind, but intelligent" and that it "commences with the conviction of the mind based on adequate evidence...", which McGrath sees as "a good and reliable definition, synthesizing the core elements of the characteristic Christian understanding of faith".

American biblical scholar Archibald Thomas Robertson (1863–1934) stated that the Greek word used for "faith" in the New Testament (over two hundred forty times), and rendered "assurance" in, is "an old verb meaning 'to furnish', used regularly by Demosthenes for bringing forward evidence." Tom Price (Oxford Centre for Christian Apologetics) affirms that when the New Testament talks about faith positively it only uses words derived from the Greek root [] which means "to be persuaded".

British Christian apologist John Lennox argues that "faith conceived as a belief that lacks warrant is very different from faith conceived as a belief that has warrant". He states that "the use of the adjective 'blind' to describe 'faith' indicates that faith is not necessarily, or always, or indeed normally, blind". "The validity, or warrant, of faith or belief depends on the strength of the evidence on which the belief is based." "We all know how to distinguish between blind faith and evidence-based faith. We are well aware that faith is only justified if there is evidence to back it up." "Evidence-based faith is the normal concept on which we base our everyday lives."

Peter S. Williams holds that "the classic Christian tradition has always valued rationality and does not hold that faith involves the complete abandonment of reason while believing in the teeth of evidence". Quoting Moreland, faith is defined as "a trust in and commitment to what we have reason to believe is true".

Regarding doubting Thomas in, Williams points out that "Thomas wasn't asked to believe without evidence". He was asked to believe based on the other disciples' testimony. Thomas initially lacked the first-hand experience of the evidence that had convinced them... Moreover, the reason John gives for recounting these events is that what he saw is evidence... Jesus did many other miraculous signs in the presence of his disciples... But these are written that you may believe that Jesus is the Christ, the son of God, and that believing ye might have life in his name. ."

Concerning doubting Thomas, Michael R. Allen wrote: "Thomas's definition of faith implies adherence to conceptual propositions for the sake of personal knowledge, knowledge of and about a person qua person".

Kenneth Boa and Robert M. Bowman Jr. describe a classic understanding of faith that is referred to as evidentialism, and which is part of a larger epistemological tradition called classical foundationalism, which is accompanied by deontologism, which holds that humans must regulate their beliefs following evidentialist structures. They show how this can go too far, and Alvin Plantinga While Plantinga upholds that faith may be the result of evidence testifying to the reliability of the source (of the truth claims), yet he sees having faith as being the result of hearing the truth of the gospel with the internal persuasion by the Holy Spirit moving and enabling him to believe. "Christian belief is produced in the believer by the internal instigation of the Holy Spirit, endorsing the teachings of Scripture, which is itself divinely inspired by the Holy Spirit. The result of the work of the Holy Spirit is faith."

Catholicism
The four-part Catechism of the Catholic Church (CCC) gives Part One to "The Profession of Faith". This section describes the content of faith. It elaborates and expands, particularly upon the Apostles' Creed. CCC 144 initiates a section on the "Obedience of Faith".

In the theology of Pope John Paul II, faith is understood in personal terms as a trusting commitment of person to person and thus involves Christian commitment to the divine person of Jesus Christ.

Methodism
In Methodism, faith plays an important role in justification, which occurs during the New Birth. The Emmanuel Association, a Methodist denomination in the conservative holiness movement, teaches: "Living faith is the gift of God imparted to the obedient heart through the Word of God, and the ministry of the Holy Ghost . This faith becomes effective as it is exercised by man with the aid of the Spirit, which aid is always assured when the heart has met the divine condition . Living faith is to be distinguished from intellectual confidence which may be in the possession of any unawakened soul."

The Church of Jesus Christ of Latter-day Saints
The Articles of Faith of the Church of Jesus Christ of Latter-day Saints states that "faith in the Lord Jesus Christ" is the first principle of the gospel.

Some alternative, yet impactful, ideas regarding the nature of faith were presented by church founder Joseph Smith in a collection of sermons, which are now published as the Lectures on Faith.

 * Lecture 1 explains what faith is;
 * Lecture 2 describes how mankind comes to know about God;
 * Lectures 3 and 4 make clear the necessary and unchanging attributes of God;
 * Lecture 5 deals with the nature of God the Father, his Son Jesus Christ, and the Holy Ghost;
 * Lecture 6 proclaims that the willingness to sacrifice all earthly things is a prerequisite to gaining faith in salvation;
 * Lecture 7 treats the fruits of faith—perspective, power, and eventually perfection.

Buddhism
Faith in Buddhism refers to a serene commitment to the practice of the Buddha's teaching and trust in enlightened or highly developed beings, such as Buddhas or bodhisattvas (those aiming to become a Buddha). Buddhists usually recognize multiple objects of faith, but many are especially devoted to one particular object of faith, such as one particular Buddha.

In early Buddhism, faith was focused on the Three Jewels or Refuges, namely, Gautama Buddha, his teaching (the Dhamma), and the community of spiritually developed followers, or the monastic community seeking enlightenment (the Sangha). Although offerings to the monastic community were valued highest, early Buddhism did not morally condemn peaceful offerings to deities. A faithful devotee was called upāsaka or upāsika, for which no formal declaration was required. In early Buddhism, personal verification was valued highest in attaining the truth, and sacred scriptures, reason, or faith in a teacher were considered less valuable sources of authority. As important as faith was, it was a mere initial step to the path to wisdom and enlightenment, and was obsolete or redefined at the final stage of that path.

While faith in Buddhism does not imply "blind faith", Buddhist practice nevertheless requires a degree of trust, primarily in the spiritual attainment of Gautama Buddha. Faith in Buddhism can still be described as faith in the Three Jewels (the Buddha, Dharma and Sangha). It is intended to lead to the goal of enlightenment, or bodhi, and Nirvana. Volitionally, faith implies a resolute and courageous act of will. It combines the steadfast resolution that one will do a thing with the self-confidence that one can do it.

In the later stratum of Buddhist history, especially Mahāyāna Buddhism, faith was given a much more important role. The concept of the Buddha Nature was developed, as devotion to Buddhas and bodhisattvas residing in Pure Lands became commonplace. With the arising of the cult of the Lotus Sūtra, faith gained a central role in Buddhist practice, which was further amplified with the development of devotion to the Amitabha Buddha in Pure Land Buddhism. In the Japanese form of Pure Land Buddhism, under the teachers Hōnen and Shinran, only entrusting faith toward the Amitabha Buddha was believed to be a fruitful form of practice, as the practice of celibacy, morality, and other Buddhist disciplines were dismissed as no longer effective in this day and age, or as contradicting the virtue of faith.Harvey2013 Faith was defined as a state similar to enlightenment, with a sense of self-negation and humility.

Thus, the role of faith increased throughout Buddhist history. However, from the nineteenth century onward, Buddhist modernism in countries like Sri Lanka and Japan, and also in the West, has downplayed and criticized the role of faith in Buddhism. Faith in Buddhism still has a role in modern Asia and the West but is understood and defined differently than in traditional interpretations. Within the Dalit Buddhist Movement communities, taking refuge is defined not only as a religious, but also a political choice.

Hinduism
Bhakti (भक्ति) literally means "attachment, participation, fondness for, homage, faith, love, devotion, worship, purity". It was originally used in Hinduism, referring to devotion and love for a personal god or a representational god by a devotee. In ancient texts such as the Shvetashvatara Upanishad, the term simply means participation, devotion, and love for any endeavor, while in the Bhagavad Gita, it connotes one of the possible paths of spirituality and towards moksha, as in.

Ahimsa, also referred to as nonviolence, is a fundamental tenet of Hinduism that advocates harmonious and peaceful co-existence and evolutionary growth in grace and wisdom for all humankind unconditionally.

In Hinduism, most of the Vedic prayers begins with the chants of Om. Om is the Sanskrit symbol that amazingly resonates the peacefulness ensconced within one's higher self. Om is considered to have a profound effect on the body and mind of the one who chants and also creates a calmness, serenity, healing, strength of its own to prevail within and also in the surrounding environment.

Islam
In Islam, a believer's faith in the metaphysical aspects of Islam is called (الإيمان), which is complete submission to the will of God, not unquestioning or blind belief. A man must build his faith on well-grounded convictions beyond any reasonable doubt and above uncertainty. According to the Quran, must be accompanied by righteous deeds and the two together are necessary for entry into Paradise. In the Hadith of Gabriel, in addition to Islam and  form the three dimensions of the Islamic religion.

Muhammad referred to the six axioms of faith in the Hadith of Gabriel: " is that you believe in God and His Angels and His Books and His Messengers and the Hereafter and the good and evil fate [ordained by your God]." The first five are mentioned together in the Qur'an. The Quran states that faith can grow with remembrance of God. The Qur'an also states that nothing in this world should be dearer to a true believer than faith.

Judaism
Judaism recognizes the positive value of (generally translated as "faith", or "trust in God") and the negative status of the  (heretic), but faith is not as stressed or as central as it is in some other religions, especially Christianity or Islam. Faith could be a necessary means for being a practicing religious Jew, but the emphasis is placed on true knowledge, true prophecy, and practice rather than on faith itself. Very rarely does it relate to any teaching that must be believed. Judaism does not require one to explicitly identify God (a key tenet of Christian faith, which is called Avodah Zarah (foreign worship) in Judaism, a minor form of idol worship, a big sin and strictly forbidden to Jews). Rather, in Judaism, one is to honor a (personal) idea of God, supported by the many principles quoted in the Talmud to define Judaism, mostly by what it is not. Thus there is no established formulation of Jewish principles of faith which are mandatory for all (observant) Jews.

In the Jewish scriptures, trust in God – – refers to how God acts toward his people and how they are to respond to him; it is rooted in the everlasting covenant established in the Torah, notably Deuteronomy 7:9:

"Know therefore that the LORD thy God, He is God; the faithful God, who keepeth covenant and mercy with them that love Him and keep His commandments to a thousand generations;"

The specific tenets that compose required belief and their application to the times have been disputed throughout Jewish history. Today many, but not all, Orthodox Jews have accepted Maimonides's Thirteen Principles of Belief.

A traditional example of as seen in the Jewish annals is found in the person of Abraham. On several occasions, Abraham both accepts statements from God that seem impossible and offers obedient actions in response to direction from God to do things that seem implausible. The Talmud describes how a thief also believes in G‑d: On the brink of his forced entry, as he is about to risk his life—and the life of his victim—he cries out with all sincerity, "G‑d help me!" The thief has faith that there is a G‑d who hears his cries, yet it escapes him that this G‑d may be able to provide for him without requiring that he abrogate G‑d's will by stealing from others. For to affect him in this way he needs study and contemplation.

Sikhism
Faith is not a religious concept in Sikhism. However, the five Sikh symbols, known as Kakaars or Five Ks (in Punjabi known as or ), are sometimes referred to as the Five articles of Faith. The articles include (uncut hair),  (small wooden comb),  (circular steel or iron bracelet),  (sword/dagger), and  (special undergarment). Baptised Sikhs are bound to wear those five articles of faith, at all times, to save them from bad company and keep them close to God.

Baháʼí Faith
In the Baháʼí Faith, faith is meant, first, as conscious knowledge, second, as the practice of good deeds, and ultimately as the acceptance of the divine authority of the Manifestations of God. In the religion's view, faith and knowledge are both required for spiritual growth. Faith involves more than outward obedience to this authority, but also must be based on a deep personal understanding of religious teachings.

Secular faith
Secular faith refers to a belief or conviction that is not based on religious or supernatural doctrines. Secular faith can arise from a wide range of sources and can take many forms, depending on the individual's beliefs and experiences, including:

 * Philosophy: Many secular beliefs are rooted in philosophical ideas, such as humanism or rationalism. These belief systems often emphasize the importance of reason, ethics, and human agency, rather than relying on supernatural or religious explanations.
 * Personal values and principles: People may develop secular faith based on their own values and principles, such as a belief in social justice or environmentalism.
 * Community and culture: Secular faith can also be influenced by the values and beliefs of a particular community or culture. For example, some people may have faith in the principles of democracy, human rights, or freedom of expression.

Epistemological analysis
The epistemological study focuses on epistemic justification, the rationality of belief, and various related issues. A justified belief is a belief that is well-supported by evidence and reasons, and that is arrived at through a reliable and trustworthy process of inquiry.

Faith is often regarded as a form of belief that may not necessarily rely on empirical evidence. However, when religious faith does make empirical claims, these claims need to undergo scientific testing to determine their validity. On the other hand, some beliefs may not make empirical claims and instead focus on non-empirical issues such as ethics, morality, and spiritual practices. In these cases, it may be necessary to evaluate the validity of these beliefs based on their internal coherence and logical consistency, rather than empirical testing.

There is a wide spectrum of opinion concerning the epistemological validity of faith — that is, whether it is a reliable way to acquire true beliefs.

Fideism
Fideism is considered to be a philosophical position rather than a comprehensive epistemological theory. It maintains that faith is independent of reason, or that reason and faith are hostile to each other and faith is superior at arriving at particular truths (see natural theology). Fideism is not a synonym for religious belief but describes a particular philosophical proposition concerning the relationship between faith's appropriate jurisdiction at arriving at truths, contrasted against reason. It states that faith is needed to determine some philosophical and religious truths, and it questions the ability of reason to arrive at all truth. The word and concept had its origin in the mid to late-19th century by way of Catholic thought, in a movement called Traditionalism. The Roman Catholic Magisterium has, however, repeatedly condemned fideism.

Critics of fideism suggest that it is not a justified or rational position from an epistemological standpoint. Fideism holds that religious beliefs cannot be justified or evaluated based on evidence or reason and that faith alone is a sufficient basis for belief. This position has been criticized because it leads to dogmatism, irrationality, and a rejection of the importance of reason and evidence in understanding the world.

William Alston argues that while faith is an important aspect of religious belief, it must be grounded in reason and evidence to be justified.

Religious epistemology
Religious epistemologists formulated and defended reasons for the rationality of accepting belief in God without the support of an argument. Some religious epistemologists hold that belief in God is more analogous to belief in a person than belief in a scientific hypothesis. Human relations demand trust and commitment. If belief in God is more like belief in other persons, then the trust that is appropriate to persons will be appropriate to God. American psychologist and philosopher William James offers a similar argument in his lecture The Will to Believe.

Foundationalism is a view about the structure of justification or knowledge. Foundationalism holds that all knowledge and justified belief are ultimately based upon what are called properly basic beliefs. This position is intended to resolve the infinite regress problem in epistemology. According to foundationalism, a belief is epistemically justified only if it is justified by properly basic beliefs. One of the significant developments in foundationalism is the rise of reformed epistemology.

Reformed epistemology is a view about the epistemology of religious belief, which holds that belief in God can be properly basic. Analytic philosophers Alvin Plantinga and Nicholas Wolterstorff develop this view. Plantinga holds that a person may rationally believe in God even though the person does not possess sufficient evidence to convince an agnostic. One difference between reformed epistemology and fideism is that the former requires defense against known objections, whereas the latter might dismiss such objections as irrelevant. Plantinga developed reformed epistemology in Warranted Christian Belief as a form of externalism that holds that the justification-conferring factors for a belief may include external factors.

Some theistic philosophers have defended theism by granting evidentialism but supporting theism through deductive arguments whose premises are considered justifiable. Some of these arguments are probabilistic, either in the sense of having weight but being inconclusive or in the sense of having a mathematical probability assigned to them. Notable in this regard are the cumulative arguments presented by British philosopher Basil Mitchell and analytic philosopher Richard Swinburne, whose arguments are based on Bayesian probability. In a notable exposition of his arguments, Swinburne appeals to an inference for the best explanation.

Professor of Mathematics and philosopher of science at University of Oxford John Lennox justifies his religious belief in Jesus's resurrection and miracles by believing God's capability of breaking the commonly recognized law of nature. John Lennox has stated, "Faith is not a leap in the dark; it's the exact opposite. It's a commitment based on evidence… It is irrational to reduce all faith to blind faith and then subject it to ridicule. That provides a very anti-intellectual and convenient way of avoiding intelligent discussion." He criticises Richard Dawkins as a famous proponent of asserting that faith equates to holding a belief without evidence, thus that it is possible to hold belief without evidence, for failing to provide evidence for this assertion.

Critics of reformed epistemology argue that it fails to provide a compelling justification for belief in God and that it is unable to account for the diversity of religious belief and experience. They also argue that it can lead to a kind of epistemic relativism, in which all religious beliefs are considered equally valid and justified, regardless of their content or coherence. Despite these criticisms, reformed epistemology has been influential in the contemporary philosophy of religion and continues to be an active area of debate and discussion.

Empirical claims
Many religious beliefs are intended to be metaphorical or symbolic, but there are also religious beliefs that are taken quite literally by believers. For example, some Christians believe that the Earth was created in six literal days, and some Muslims believe that the Quran contains scientific facts that were not known to humans at the time of its revelation. Furthermore, even if a religious belief is intended to be metaphorical or symbolic, it can still be subject to empirical testing if it makes claims about the world. For example, the claim that the Earth is the center of the universe can be interpreted as a metaphorical representation of humanity's special place in the cosmos, but it also makes an empirical claim that can be tested by scientific observation.

Morality and faith
From a scientific perspective, morality is not dependent on faith. While some individuals may claim that their morality is rooted in their faith or religious beliefs, there is evidence to suggest that morality is also influenced by other factors, such as social and cultural norms, empathy, and reason. Studies have shown that individuals from diverse cultural and religious backgrounds tend to share many moral values, suggesting that morality is not solely dependent on faith. Additionally, research in the fields of psychology, neuroscience, and evolutionary biology has shed light on the biological and cognitive mechanisms underlying moral decision-making, providing further evidence that morality is not exclusively dependent on faith.

Criticism
Bertrand Russell wrote:

"Christians hold that their faith does good, but other faiths do harm. At any rate, they hold this about the communist faith. What I wish to maintain is that all faiths do harm. We may define 'faith' as a firm belief in something for which there is no evidence. Where there is evidence, no one speaks of 'faith'. We do not speak of faith that two and two are four or that the earth is round. We only speak of faith when we wish to substitute emotion for evidence. The substitution of emotion for evidence is apt to lead to strife, since different groups substitute different emotions. Christians have faith in the Resurrection; communists have faith in Marx's Theory of Value. Neither faith can be defended rationally, and each therefore is defended by propaganda and, if necessary, by war."

Evolutionary biologist Richard Dawkins criticizes all faith by generalizing from specific faith in propositions that conflict directly with scientific evidence. He describes faith as belief without evidence; a process of active non-thinking. He states that it is a practice that only degrades our understanding of the natural world by allowing anyone to make a claim about nature that is based solely on their personal thoughts, and possibly distorted perceptions, that does not require testing against nature, cannot make reliable and consistent predictions, and is not subject to peer review.

Philosophy professor Peter Boghossian argues that reason and evidence are the only way to determine which "claims about the world are likely true". Different religious traditions make different religious claims, and Boghossian asserts that faith alone cannot resolve conflicts between these without evidence. He gives an example of the belief held by Muslims that Muhammad (who died in the year 632) was the last prophet, and the contradictory belief held by Mormons that Joseph Smith (born in 1805) was a prophet. Boghossian asserts that faith has no "built-in corrective mechanism". For factual claims, he gives the example of the belief that the Earth is 4,000 years old. With only faith and no reason or evidence, he argues, there is no way to correct this claim if it is inaccurate. Boghossian advocates thinking of faith either as "belief without evidence" or "pretending to know things you don't know".

Friedrich Nietzsche expressed his criticism of the Christian idea of faith in passage 51 of The Antichrist: "The fact that faith, under certain circumstances, may work for blessedness, but that this blessedness produced by an idée fixe by no means makes the idea itself true, and the fact that faith actually moves no mountains, but instead raises them up where there were none before: all this is made sufficiently clear by a walk through a lunatic asylum. Not, of course, to a priest: for his instincts prompt him to the lie that sickness is not sickness and lunatic asylums not lunatic asylums. Christianity finds sickness necessary, just as the Greek spirit had need of a superabundance of health—the actual ulterior purpose of the whole system of salvation of the church is to make people ill. And the church itself—doesn't it set up a Catholic lunatic asylum as the ultimate ideal?—The whole earth as a madhouse?—The sort of religious man that the church wants is a typical décadent; the moment at which a religious crisis dominates a people is always marked by epidemics of nervous disorder; the 'inner world' of the religious man is so much like the 'inner world' of the overstrung and exhausted that it is difficult to distinguish between them; the 'highest' states of mind, held up before mankind by Christianity as of supreme worth, are actually epileptoid in form—the church has granted the name of holy only to lunatics or to gigantic frauds in majorem dei honorem...."

Gustave Le Bon emphasizes the irrational nature of faith and suggests that it is often based on emotions rather than reason. He argues that faith can be used to manipulate and control people, particularly in the context of religious or political movements. In this sense, Le Bon views faith as a tool that can be wielded by those in power to shape the beliefs and behaviors of the masses.

Classic reflections on the nature of faith

 * Martin Buber, I and Thou
 * Paul Tillich, The Dynamics of Faith

The Reformation view of faith

 * John Calvin, The Institutes of the Christian Religion, 1536
 * R.C. Sproul, Faith Alone, Baker Books, 1 February 1999, ISBN 9780801058493

title: Faith