# Friction FAQs:

Q: Is friction the force resisting the relative motion of solid surfaces?

A: Yes, and fluid layers, and material elements sliding against each other.

Q: Is friction the force resisting motion between the elements making up a solid material while it undergoes deformation?

A: Yes.

Q: Is friction a particularly dangerous condition arising due to varying friction on either side of a car?

A: Yes.

Q: Is friction a component of the science of tribology?

A: Yes.

Q: Is friction independent of the apparent area of contact?

A: Yes.

Q: Is friction subdivided into static friction between non-moving surfaces?

A: Yes, and kinetic friction between moving surfaces.

Q: Is friction now understood, in many cases, to be primarily caused by chemical bonding between the surfaces, rather than interlocking asperities?

A: Yes, however, in many other cases roughness effects are dominant, for example in rubber to road friction.

Q: Is friction a component of drag?

A: Yes, and the force resisting the motion of a fluid across the surface of a body.

Q: Is friction small whereas the coefficient of friction for braking friction is designed to be large by choice of materials for brake pads?

A: Yes.

Q: Is friction a case of fluid friction where a fluid separates two solid surfaces?

A: Yes.

Q: Is friction the force resisting motion between the elements making up a solid material while it undergoes deformation?

A: Yes.

Q: Was friction further developed by Charles-Augustin de Coulomb?

A: Yes, 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; and the length of time that the surfaces remained in contact. 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.

Q: Is friction always in the direction opposite the motion?

A: Yes, and does negative work.

Q: Is friction an important factor in many engineering disciplines?

A: Yes.

Q: Is friction by using a lubricant?

A: Yes, such as oil, water, or grease, which is placed between the two surfaces, often dramatically lessening the coefficient of friction.

Q: Is friction not a function of mass or volume?

A: Yes, it depends only on the material.

Q: Is friction a physical property observed from the forces acting on a belt wrapped around a pulley?

A: Yes, when one end is being pulled.

Q: Is friction no longer applicable—the friction between the two surfaces is then called kinetic friction?

A: Yes.

Q: Is friction 'static friction' between non-moving surfaces?

A: Yes, and kinetic friction between moving surfaces.

Q: Is friction typically denoted as μk?

A: Yes, and is usually less than the coefficient of static friction for the same materials.

Q: Is friction usually larger than that of kinetic friction?

A: Yes, in some sets the two coefficients are equal, such as teflon-on-teflon.

Q: Is friction used to mix and join materials such as in the process of friction welding?

A: Yes.

Q: Is friction friction between two or more solid objects that are not moving relative to each other?

A: Yes.

Q: Is friction directly proportional to the applied load?

A: Yes.

Q: Was friction the force necessary to tear the adhering surfaces apart?

A: Yes.

Q: Is friction the product of the inter-surface shear stress and the contact area?

A: Yes.

Q: Is friction desirable and important in supplying traction to facilitate motion on land?

A: Yes.

Q: Is friction a classic example of thermodynamic irreversibility?

A: Yes.

Q: Is friction a non-conservative force - work done against friction is path dependent?

A: Yes.

Q: Is friction caused by viscous drag in the boundary layer around the object?

A: Yes.

Q: Is friction made in Coulomb's friction law?

A: Yes, although this distinction was already drawn by Johann Andreas von Segner in 1758.

Q: Is friction the force that prevents a car wheel from slipping as it rolls on the ground?

A: Yes.

Q: Is friction an empirical measurement – it has to be measured experimentally?

A: Yes, and cannot be found through calculations.

Q: Is friction always exerted in a direction that opposes movement or potential movement between the two surfaces?

A: Yes.

Q: Is friction discovered by Leonardo da Vinci in 1493?

A: Yes, and a pioneer in tribology, but the laws documented in his notebooks, were not published and remained unknown.

Q: Is friction not itself a fundamental force?

A: Yes.

Q: Is friction independent of the sliding velocity?

A: Yes.

Q: Is friction a case of fluid friction where a lubricant fluid separates two solid surfaces?

A: Yes.