What is a Frictional force?

Frictional Force Definition: Frictional force refers to the force generated by two surfaces that contacts and slide against each other. These forces are mainly affected by the surface texture and amount of force impelling them together. The angle and position of the object affect the amount of frictional force.

If an object is placed flat against an object, then the frictional force will be equal to the weight of the object.

If an object is pushed against the surface, then the frictional force will be increased and becomes more than the weight of the object.

Frictional force formula

The maximum amount of friction force that a surface can apply upon an object can be easily calculated with the use of given formula:

Ffrict = µ • Fnorm

Frictional force types

There are different types of frictional forces:

1.Dry Friction - It is the friction exists between any two objects that are in mechanical contact and is normally assumed to be the influence of dry friction force. This force is generated in the tangential direction of the plane of contact, and both the objects prevent the movements between the surfaces.

2.Fluid Friction - Fluid Friction is the force that obstructs the flow of fluid. It is a situation where the fluid provides resistance between the two surfaces. If both the surfaces offer high resistance then it is known as high viscous and, generally we call them as greasy.

Examples of Fluid Friction:

  1. To avoid creaking sounds from doors, we lubricate the door hinges which leads to the smooth functioning of door hinges.
  2. When you drop the ball in full bucket of water, water splashes out of the bucket and is all because of buoyancy of fluid. 

Problems on Frictional Force:

 Problem 1– A 50N amount of force is applied to the 6 kg of box. If the coefficient of friction is 0, 3, what will be the acceleration of the box?

Solution 1– Fnormal =60N-40N=20N

Friction force is –  Ffriction=µ.Fnormal = 0, 3.20N=6N

Net force in –Y to Y = zero,

However, in –X +X direction net force is not zero





Problem 2– A block of mass M = 10 kg is placed on a surface inclined at angle θ = 45°. Given that the coefficient of static friction is μs = 0.5 between block and the surface.

  • What will be the minimum force F necessary to prevent slipping?
  • What will be the maximum force F that can be exerted without causing the block to slip?

Solution 2-The minimum force required to prevent slipping is the minimum force that will prevent the block from sliding down the incline.

Fmin = 10gsin(45°)—10gcos(45°)x0.5.

The maximum force that can be exerted without causing the block to slip is the maximum force that can be exerted without causing the block to slide up the incline.

Fmax = 10gsin(45°)+10gcos(45°)x0.5.

Fmin = 34.65 N, Fmax = 103.94 N