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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 ...
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.
Tribology is the science and engineering of understanding friction, lubrication and wear phenomena for interacting surfaces in relative motion.It is highly interdisciplinary, drawing on many academic fields, including physics, chemistry, materials science, mathematics, biology and engineering. [1]
The friction produced in the contact between the ball and the surface results in a horizontal force on the surface and a rotational force on the ball. Frictional force is determined by finding the rotational speed of the ball using high speed photography or by measuring the force on the horizontal surface.
[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.
The SI unit of force is the newton (symbol N), which is the force required to accelerate a one kilogram mass at a rate of one meter per second squared, or kg·m·s −2.The corresponding CGS unit is the dyne, the force required to accelerate a one gram mass by one centimeter per second squared, or g·cm·s −2. A newton is thus equal to ...
The British imperial units and U.S. customary units for both energy and work include the foot-pound force (1.3558 J), the British thermal unit (BTU) which has various values in the region of 1055 J, the horsepower-hour (2.6845 MJ), and the gasoline gallon equivalent (about 120 MJ).