At the relative movement of two bodies between them there is a friction. It can also arise at the movement in the gaseous or liquid environment. Friction can both disturb, and to promote the normal movement. As a result of this phenomenon the interacting bodies are affected by friction force.
Instruction
1. The most general case considers friction slidings force when one of bodies is fixed and is based, and another slides on its surface. From a body on which the moving body slides the last is affected by force of reaction of a support directed perpendicular to the sliding plane. This force is designated by the letter N.Telo can as well is based concerning the fixed body. Then friction force operating on it with Ftr <? N.? - it is dimensionless coefficient of friction. It depends on materials of the rubbing surfaces, degree of their otshlifovka and some other factors.
2. In case of the movement of a body concerning the surface of the fixed body friction force of sliding becomes equal works of coefficient of friction on force of reaction of a support: Ftr =? N.
3. If the surface is located horizontally, then force of reaction of a support on the module is equal to the gravity operating on a body that is N = to mg where m is the mass of the sliding body, g is the acceleration of gravity equal to about 9.8 m / (с^2) on Earth. From here, Ftr =? mg.
4. Let now the body be affected by constant force F> with Ftr =? N parallel to a surface of the adjoining bodies. When sliding a body, the resulting force component will be equal in the horizontal direction to F-Ftr. Then under the second law of Newton, acceleration of a body will be connected with the resulting force on a formula: a = (F-Ftr)/m. From here, Ftr = F-ma. Acceleration of a body can be found for kinematic reasons.
5. Often considered special case of friction force is shown when sliding a body from the fixed inclined plane. Let? - the tilt angle of the plane and let a body slides off evenly, that is without acceleration. Then the equations of the movement of a body will look so: N = mg*cos?, mg*sin? = Ftr =? N. Then from the first equation of the movement friction force can be expressed as Ftr =? mg*cos?. If the body moves on the inclined plane with acceleration of a, then the second equation the movement will have an appearance: mg*sin? - Ftr = ma. Then Ftr = mg*sin? - ma.