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A contact force is any force that occurs as a result of two objects making contact with each other. [1] Contact forces are very common and are responsible for most visible interactions between macroscopic collections of matter. Pushing a car or kicking a ball are some of the everyday examples where contact forces are at work.
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 ...
This result is due to a number of discontinuities in the behavior of rigid bodies and the discontinuities inherent in the Coulomb friction law, especially when dealing with large coefficients of friction. [2] There exist, however, simple examples which prove that the Painlevé paradoxes can appear even for small, realistic friction.
For example, a free body diagram of a block sitting upon an inclined plane can illustrate the combination of gravitational force, "normal" force, friction, and string tension. [note 4] Newton's second law is sometimes presented as a definition of force, i.e., a force is that which exists when an inertial observer sees a body accelerating.
Other examples include many polymer solutions (which exhibit the Weissenberg effect), molten polymers, many solid suspensions, blood, and most highly viscous fluids. Newtonian fluids are named after Isaac Newton , who first used the differential equation to postulate the relation between the shear strain rate and shear stress for such fluids.
In static friction there is coupling between elastic strains, polarization and surface charge which contributes to the frictional force. [82] In sliding friction, [108] when asperities contact [38] and there is charge transfer, some of the charge returns as the contacts are released, some does not [109] and will contribute to the ...
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.
As an example, assume that friction is the only force acting on the particle, and that it may be modeled as a function of the velocity of the particle, for example: =, where λ is a positive constant, the negative sign states that the force is opposite the sense of the velocity. Then the equation of motion is