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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 μ k, and is usually less than the coefficient of static friction for the same materials.
The former is concerned with static friction (also known as "stiction" [3]) or "limiting friction", whilst the latter is dynamic friction, also called "sliding friction". For steel on steel, the coefficient of friction can be as high as 0.78, under laboratory conditions, but typically on railways it is between 0.35 and 0.5, [4] whilst under ...
Sliding friction (also called kinetic friction) is a contact force that resists the sliding motion of two objects or an object and a surface. Sliding friction is almost always less than that of static friction; this is why it is easier to move an object once it starts moving rather than to get the object to begin moving from a rest position.
This theory is exact for the situation of an infinite friction coefficient in which case the slip area vanishes, and is approximative for non-vanishing creepages. It does assume Coulomb's friction law, which more or less requires (scrupulously) clean surfaces. This theory is for massive bodies such as the railway wheel-rail contact.
The International Table Tennis Federation specifies that the ball shall bounce up 24–26 cm when dropped from a height of 30.5 cm on to a standard steel block, [7] implying a COR of 0.887 to 0.923. The International Basketball Federation (FIBA) rules require that the ball rebound to a height of between 1035 and 1085 mm when dropped from a ...
Kinetic friction on the other hand, occurs when two objects are undergoing relative motion, as they slide against each other. The force F k exerted between the moving objects is equal in magnitude to the product of the normal force N and the coefficient of kinetic friction μ k: | | =. Regardless of the mode, friction always acts to oppose the ...
is the rolling resistance coefficient or coefficient of rolling friction with dimension of length, and N {\displaystyle N} is the normal force (equal to W , not R , as shown in figure 1). The above equation, where resistance is inversely proportional to radius r {\displaystyle r} seems to be based on the discredited "Coulomb's law" (Neither ...
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