Friction can be defined as that force which offers resistance to two surfaces that are moving against each other. It is mainly due to the intermolecular or IM attractions that occur between the particles of the two adjoining surfaces. There are different types of this force namely static, sliding, rolling and fluid. Let us understand this in detail.
Static friction occurs when an object starts to move which means that for such friction to occur the object has to overcome the static force friction and start moving. Sliding friction occurs when an object moves on the surface of the other object present. This is called ‘slide’. This results in opposing the movement or slide of the two objects. Additionally, rolling friction occurs when an object rolls on another surface or object. Lastly, fluid friction occurs when a fluid exerts a friction force on the object. It can either be air friction where the medium of travel is air or it can be viscous friction where the medium is water.
There are some variables on which the friction depends on. The first one is the normal force or. It is the force between the adjacent surfaces that slide against each other. Second, it depends on the coefficient of Friction which is denoted by µ. It gives us the nature of the surfaces that slide against each other.
What is the Friction Formula?
Friction is the resisting force that prevents rigid surfaces, fluid layers, and material elements from slipping against each other from moving in the same direction. Friction between two surfaces transforms kinetic energy into thermal energy, or work to heat, as they shift relative to each other. Friction is beneficial and essential for providing traction and facilitating movement on the ground. For acceleration, deceleration, and changing direction, most land vehicles depend on friction. Sudden traction failure can result in a loss of control and an accident.
Types of Friction
There are four types of friction:
Between a stationary object and the surface on which it is resting, static friction occurs.
When two things slide against each other, sliding friction occurs.
The resistive force that slows the motion of a moving ball or wheel is known as rolling friction. It's often referred to as rolling resistance.
The friction that occurs between the layers of fluid as they are moving relative to Each other is known as fluid friction.
Friction Force Formula
Consider a solid block resting on a horizontal surface. When a force of ‘P’ is applied to the block, the block does not move along the force applied. This is because the frictional
force is more than the applied force which balances the solid block. Here the frictional force also increases accordingly when the applied force is increased. Once the applied force reaches more than the frictional force then. The solid block slides over the horizontal surface. This force when the body begins to move is called limiting friction.
This friction is called static friction because one body is sliding over the other which is stationary.
To derive the static friction force formula we have to consider all the forces acting on the body.
The static friction equation or the coefficient of friction formula or force of friction equation is given as follows
Here the static frictional force is directly proportional to the normal force acting on the body.
F α N
F = μN
Where F is the maximum force of static friction.
N is the normal force which is equal to the mass of the body multiplied by the acceleration due to gravity.
N = mg
μ is the coefficient of friction.
Rolling Friction Formula
Consider a ball placed on the flat horizontal surface. When a ball is given a motion to move forward the frictional force from the ground makes the ball stop. This friction is known as rolling friction.
The rolling friction formula or the coefficient of friction formula for rolling is given as follows
F = Crr N
Where F is the rolling resistance force.
Crr is the dimensionless rolling resistance coefficient or the coefficient of rolling
N is the normal force that is the force perpendicular to the surface on which the ball is rolling.
Friction Force Formula for an Inclined Plane
Consider a mass m that is lying on an inclined plane. If the mass is moving down the plane, the frictional force F will act up the plane.
The friction formula or the coefficient of friction equation or angle of friction formula is given as follows:
F = μN
Where F = Frictional force.
N = normal force exerted on the body by the plane due to the force of gravity = mg Cos θ
μ = coefficient of
friction = tan θ
θ = Angle of inclination of the plane over the body slides.
The optimum value of θ for static friction can be obtained by steadily rising θ until the mass begins to move. This is known as the limiting angle of repose.
Problems on Friction Formula
1) A boy pulls a body of mass 50Kg resting on a flat horizontal surface. Calculate the frictional force if the coefficient of friction is 0.3.
Here it is given that mass of the body m = 50Kg and coefficient of friction =0.3
The friction formula is given as
F = μN
Here N is the normal force given by the formula
N = mg
g is the acceleration due to gravity = 9.81 m/s2
So N = 50 × 9.81 = 5395.5
Kgm/s2 = 5395.5
N , Now substituting the values in the friction formula we get the required frictional force
F = 0.3 × 5395.5 = 1618.65 N
2) A boy is rolling a ball over the flat horizontal surface. The mass of the ball is 10 Kg and the coefficient of rolling friction 0.2. Calculate the rolling resistance force.
mass of the ball is m = 10 Kg
Coefficient of rolling friction, Crr = 0.2
The rolling resistance force is given by the formula
F = Crr N
Here N is the normal force of the body which is given as N = mg
Here g is the acceleration
due to gravity = 9.81 m/s2
N = 10 × 9.81 = 98.1 Kgm/s2 = 98.1 N.
Substituting the values we will get the required rolling resistance force
F = 0.2 × 98.1 = 19.62 N
The friction force prevents one rigid object from slipping or rolling over another. Frictional forces, such as the traction required to walk without falling, may be helpful, but they also create significant resistance to motion. Around 20% of an automobile's engine power is used to overcome frictional forces in the moving parts. The forces of attraction, known as adhesion, between the contact regions of the surfaces, which are often microscopically irregular, tend to be the primary cause of friction between metals. Shearing these welded junctions cause friction, as do the irregularities of the rough surface plowing through the softer surface.