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the force of friction acting between two sliding surfaces is proportional to the load pressing the surfaces together; the force of friction is independent of the apparent area of contact between the two surfaces. Although not universally applicable, these simple statements hold for a surprisingly wide range of systems. [4]
where is the force (positive in compression), is the total surface energy of both surfaces per unit area, and is the equilibrium separation of the two atomic planes. The Bradley model applied the Lennard-Jones potential to find the force of adhesion between two rigid spheres.
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 ...
[1] [2] This can be divided into compressive and adhesive forces in the direction perpendicular to the interface, and frictional forces in the tangential direction. Frictional contact mechanics is the study of the deformation of bodies in the presence of frictional effects, whereas frictionless contact mechanics assumes the absence of such effects.
Part of the energy needed for this deformation is recovered (elastic deformation), some is not and goes into heating the tires. The energy which is not recovered contributes to the back force, a process called rolling friction. Similar to rolling friction there are energy terms in charge transfer, which contribute to friction.
Creeping flow past a falling sphere in a fluid (e.g., a droplet of fog falling through the air): streamlines, drag force F d and force by gravity F g. At terminal (or settling) velocity, the excess force F e due to the difference between the weight and buoyancy of the sphere (both caused by gravity [7]) is given by:
The small black vector arrow represents the frictional force caused by the bar sliding across the second bar (grey). In mechanics, friction torque is the torque caused by the frictional force that occurs when two objects in contact move. [1] Like all torques, it is a rotational force that may be measured in newton meters or pounds-feet.
Coulomb damping absorbs energy with friction, which converts that kinetic energy into thermal energy, i.e. heat. Coulomb friction considers this under two distinct modes: either static, or kinetic. Static friction occurs when two objects are not in relative motion, e.g. if both are stationary.