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The maximum possible friction force between two surfaces before sliding begins is the product of the coefficient of static friction and the normal force: =. When there is no sliding occurring, the friction force can have any value from zero up to F max {\displaystyle F_{\text{max}}} .
Figure 2: Weight (W), the frictional force (F r), and the normal force (F n) acting on a block.Weight is the product of mass (m) and the acceleration of gravity (g).In the case of an object resting upon a flat table (unlike on an incline as in Figures 1 and 2), the normal force on the object is equal but in opposite direction to the gravitational force applied on the object (or the weight of ...
[30] [31] Assuming a model of shearing welded contacts in tribological interactions, this ubiquitously observed linearity between contact area and pressure can also be considered the origin of the linearity of the relationship between static friction and applied normal force. [29]
In systems with significant nonuniform stress fields, the macroscopic static friction coefficient depends on the external pressure, system size, or shape because local slip occurs before the system slides. [18] The following table shows the values of the static and dynamic friction coefficients for common materials:
Where N, the normal force, is equal to the weight (mass x gravity) of the sitting mass (m T) and F, the loading force, is equal to the weight (mass x gravity) of the hanging mass (m H). To determine the kinetic coefficient of friction the hanging mass is increased or decreased until the mass system moves at a constant speed.
The frictional force is equivalent to the multiplication product of the coefficient of static friction and the Normal Force or : m g sin θ = N μ {\displaystyle mg\sin \theta =N\mu } m g sin θ = μ m g cos θ {\displaystyle mg\sin \theta =\mu mg\cos \theta }
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 static friction force will exactly oppose forces applied to an object parallel to a surface up to the limit specified by the coefficient of static friction multiplied by the normal force (). In other words, the magnitude of the static friction force satisfies the inequality: 0 ≤ F s f ≤ μ s f F N . {\displaystyle 0\leq \mathbf {F ...