The coefficient of static friction is the friction force between two objects when neither of the objects is moving. Coefficient of friction pdf coefficient of kinetic friction is the force between two objects when one object is moving, or if two objects are moving against one another. The coefficient of friction depends on the objects that are causing friction.
The value is usually between 0 and 1 but can be greater than 1. A value of 0 means there is no friction at all between the objects. All objects in the real world will have some friction when they touch each other. A value of 1 means the frictional force is equal to the normal force.
Some people think that the coefficient of friction can never be more than 1, but this is not true. A coefficient of friction that is more than one just means that friction is stronger than the normal force. The friction force is the force exerted by a surface when an object moves across it – or makes an effort to move across it. You can change this page. Please use the preview button before saving. The list of new changes in the wiki. This page was last changed on 6 December 2017, at 20:22.
This property can have dramatic consequences, as illustrated by the use of friction created by rubbing pieces of wood together to start a fire. Sudden reductions in traction can cause loss of control and accidents. Dry friction arises from a combination of inter-surface adhesion, surface roughness, surface deformation, and surface contamination. In the presence of friction, some energy is always lost in the form of heat.
Amontons presented the nature of friction in terms of surface irregularities and the force required to raise the weight pressing the surfaces together. 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. 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.
This actual area of contact, caused by asperities increases with pressure. The force of friction is directly proportional to the applied load. The force of friction is independent of the apparent area of contact. Kinetic friction is independent of the sliding velocity. Dry friction resists relative lateral motion of two solid surfaces in contact.
It is parallel to the surface, in a direction opposite to the net applied force. 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. In this case, the magnitude of the friction force is the product of the mass of the object, the acceleration due to gravity, and the coefficient of friction. For instance, a large aluminum block has the same coefficient of friction as a small aluminum block.