Product Code Database
A contact force is any force that occurs because of two objects making contact with each other. 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 everyday examples where contact forces are at work. In the first case the force is continuously applied to the car by a person, while in the second case the force is delivered in a short impulse.
Contact forces are often decomposed into orthogonal components, one perpendicular to the surface(s) in contact called the normal force, and one parallel to the surface(s) in contact, called the friction force.
Not all forces are contact forces; for example, the weight of an object is the force between the object and the Earth, even though the two do not need to make contact. Gravitational forces, electrical forces and magnetic forces are and can exist without contact occurring.
As for friction, it is a result of both microscopic adhesion and chemical bond formation due to the electromagnetic force, and of microscopic structures stressing into each other;Chen, Z., Khajeh, A., Martini, A., & Kim, S. H. (2019). Chemical and physical origins of friction on surfaces with atomic steps. Science advances, 5(8), eaaw0513. in the latter phenomena, in order to allow motion, the microscopic structures must either slide one above the other, or must acquire enough energy to break one another. Thus the force acting against motion is a combination of the normal force and of the force required to widen microscopic cracks within matter; the latter force is again due to electromagnetic interaction. Additionally, strain is created inside matter, and this strain is due to a combination of electromagnetic interactions (as electrons are attracted to nuclei and repelled from each other) and of Pauli exclusion principle, the latter working similarly to the case of normal force.
|
|
