Difference Between Static friction and Kinetic friction

Static friction vs Kinetic friction

Static friction and kinetic friction are two forms of friction. Friction is a very important concept when it comes to the field of mechanics of solid bodies. Friction is considered to be one of the main causes of mechanical energy loss. Therefore, a good understanding in friction is necessary to develop more efficient machinery in order to save energy. Friction, whether it is static or kinetic, plays a vital role in our day to day lives. If it is not for friction, we simply would not be able to walk or even grab a spoon. Understanding friction is very important in fields such as mechanical engineering, automobile engineering, physics and even life sciences. In this article, we are going to discuss what static friction and kinetic friction are, their definitions, how do they occur, their similarities, what factors effect static and kinetic friction and finally their differences.

Static Friction

To understand what static friction is one must first understand the concept of friction as a whole. Friction can occur in any medium. It is the resistance of the media to a relatively moving object, or an object that is attempting to move. Static friction is a sub section of dry friction. When two solid objects touch each other, there is a force resisting the relative movement of the two faces. The main cause for this resistance is the unevenness of the two faces. These faces have little peaks on the microscopic level. When peaks of one surface go into the valleys of the other surface, these objects tend to lock, restricting the relative motion. If an object placed on a flat surface is given a force parallel to the plane, the object will not move. This is due to the static friction. By the principle of force equilibrium, the static friction is equal to the force applied. Dry friction has three main laws. Amonton’s first law says the force of friction is directly proportional to the load applied. Amonton’s second law says the force of friction is independent of the contact area. The third law considers kinetic friction. It can be formulated that the force of friction is equal to the normal force to the surface times the proportionality constant. However, since friction is equal to the applied force the proportionality constant varies with the applied force, this proportionality constant is known as the coefficient of friction. There is a maximum value for the static friction, and therefore, it is the static frictional coefficient. A force, which is greater than the maximum force of friction, is required to move the object.

Kinetic Friction

Kinetic friction occurs when two touched object move relative to each other. The coulomb’s law says that the kinetic friction is independent of the sliding velocity. It is observed that the kinetic friction is little lower than the maximum static friction. This causes the imbalance feeling when an object starts to move. The kinetic friction on each surface is always opposite to the direction of movement.