# Friction

Friction in Physics is defined as a type of force that always opposes the motion of the object on which it is applied. Suppose we kick a football and it rolls for some distance and eventually it stops after rolling for some time. This is because of the friction force between the ball and the ground. Here, the force acting opposite to the motion of the ball that stops the ball is called the friction or friction force. Friction acts between two surfaces when one surface is in a state of motion.

## What is Friction?

Friction is a force that opposes the motion of the object to which it is applied. Friction is responsible for stopping of car when the accelerator is turned off. Friction is a necessary evil and is responsible for various day-to-day activities. For walking, running, and various purposes friction is necessary. Friction is a non-conservative force that is work done by the friction force is dependent on the path chosen.

For example, when we wish to stop or slow down our car or bikes, we use brakes that increase the friction in the wheel and result in the stopping of the car. Friction always works in the opposite direction of motion. In the image added below, a block resting on the floor force is applied to the box such that it moves toward the east, now the friction opposes themotion of the object and acts in the west direction.

### Unit of friction

• Friction is a type of force and so its unit is similar to the unit of force Newton (N) or ms-2.
• Its dimensional formula is [MLT-2].

## Friction Formula

An object resting on the floor on earth experiences a gravitational force on its body and that is balanced by the normal force from the ground. If an object of mass ‘m’ rests on the floor then the force it applies on the floor is,

Fg = mg

Now,

Normal Force(N) = -Fg = -mg

Friction force(F) acting on the object is given using the frictional force and the friction force is given as,

F = -Î¼mg

where,

• Î¼ is Coefficient of Friction
• m is Mass of Object
• g is Gravity of the Earth

## Coefficient of Friction

Coefficient of Friction is defined as the ratio of the frictional force and the resisting force between two surfaces. We use Greek letter mu(Î¼), to represent the coefficient of friction. Higher the coefficient of friction higher is the friction force between two surfaces.

• For rough surfaces Î¼ (coefficient of friction) is very high
• For smooth surfaces Î¼ (coefficient of friction) is very low

If the normal force acting on the body is N and the frictional force acting on the body is F then the coefficient of friction is calculated by the formula,

Î¼ = F/N

As coefficient of friction is the ratio of two or more term it is a dimension less quantity, i.e. it has no units.

## Factors Affecting Friction

Factors affecting the friction force are given below,

• When two rough surfaces come into contact, the degree of friction between them is high due to the excessive interlocking of rough surfaces.
• Because there is less interlocking between smooth surfaces when two smooth surfaces are in touch, the degree of friction between them is low.
• It is also affected by the object’s weight or the amount of force it exerts on the surface.

## Causes of Friction

The cause of friction are the irregularities on two surfaces in contact that produce friction. As a result, as one object passes over another, the irregularities on the surface become intertwined, causing friction. The rougher the surface, the more irregularities there will be and the friction will be greater. The more smoother the surface the less friction it offeres.

## Types of Friction

Friction are categorised into four types. The four types of friction are,

• Static friction
• Sliding friction
• Rolling friction
• Fluid friction

Now let’s learn the same in detail,

### Static friction

Static friction, also known as limiting frictional force, represents the resistance encountered between an object and the surface upon which it rests. To set an object in motion when it’s at rest on a surface, you must exert a force greater than the frictional force between them. This concept applies to various activities, such as walking and rock climbing.

### Sliding friction

When we move things across another surface, a force acts on the object, called sliding friction. It’s not as strong as static friction. Think of sliding a block on a table, writing with a pen, or even playing on a slideâ€”these are examples of sliding friction in action.

### Rolling friction

Rolling friction is the resistance that happens when one object is made to roll on the surface of another. It’s notably less intense than kinetic friction. You can observe rolling friction in everyday activities like roller skating and the use of ball bearings, where objects roll smoothly across surfaces.

### Fluid friction

A substance that can flow and take the shape of its container is known as a fluid. Fluid friction refers to the resistance that liquids or gases present when an object is in motion within them. To put it simply, it’s the frictional force exerted by fluids.

## Effects of Friction

Various effects of the friction observed by us in our daily lives are,

• It results in a loss of power for various machines and engines.
• We can walk, run, play, and so forth due to friction.
• It generates heat, which may be used to warm sections of an item or ourselves.
• During any operation, it generates noise, etc.

## Laws of Friction

Various laws of friction are,

• The friction between the moving item and the normal force is proportionate and perpendicular.
• Friction exists regardless of the area of contact as long as there is one.
• The object’s friction is determined by the type of surface it comes into contact with.
• The static friction coefficient is higher than the kinetic friction coefficient.
• Velocity does not affect kinetic friction.

## Application of Friction

Friction has various applications and that are added below,

• Friction is created by the movement of pistons in a cylinder.
• When matchsticks are lit, friction comes into play.
• Because there is friction between the pen and the board, writing on books and boards is feasible.
• Fixing a nail on a wall or in a wooden block is possible because of friction.
• The working of brakes in vehicles depends on friction. When brakes are applied, the rotation of the wheels is stopped by the forces of friction between the brake lining and the drum (or the wheel).
• It is the friction between the belt and the pulley that helps the rotation of various parts of a machine.

• The efficiency of a machine goes down as it has to waste a fraction of its effort in overcoming friction.
• Friction produces heat which damages the parts of a machine.
• Friction contributes to the wear and tear of the parts of a machine.
• The engine of a car seizes. If it runs short of oil. The piston and the cylinder get so hot on account of excessive friction that they may get jammed.

## Friction and Gravity

Friction force working on the body is,

F = Î¼.N

where,

• Î¼ is the Coefficient of Friction
• N is Normal Force

Now the the normal force acting on the body is,

N = m.g

The normal force is a perpendicular force applied to the surface to the body. It is acted on the body by surface under the influence of gravity in the downward direction. Gravity is the downward acceleration experienced by anybody on the surface of any planet. This is responsible for weight experienced by the body. On a flat surface weight and Normal are opposite in direction. The surface in contact produces frictional force.

## Friction and Force

friction is a type of force that opposes the motion of the object. Suppose an object moving on the floor comes to rest eventually, this is because of the friction. Generally when an object moves friction and force working on that body are opposite to each other. Suppose a force (f) works on the body then the friction force working on the body is,

Friction Force (F) = -Î¼f

where,

• sign indicates that friction force is opposite to the motion of the object
• Î¼ is Coefficient of friction

## Friction – FAQs

### 1. What is Frictional Force?

friction force is a force that oppose the motion of the object. Suppose an object moves on a surface then it eventually stops because of the fictional force.

### 2. What is the Formula of friction?

The friction force acting on the object is given as,

F = -Î¼mg

### 3. Why does Friction Produce Heat?

Friction force produces heat because of the kinetic energy of the object that is in state of motion.

### 4. Is Friction a Conservative Force or Non-Conservative Force?

friction Force is a Non-Conservative Force, as the workdone by friction force depends on the path taken.

### 5. Why is Friction a Non-Conservative Force?

Friction is a non-conservative force because the amount of work done by the friction depends on the path.

### 6. Can Friction be Zero?

No, it is impossible to have zero friction because every surface will have minor irregularities no matter how lubricated.

### 7. What is Coeeficient of Friction?

The coefficient of friction is defined as the ratio of the frictional force and the normal force acting of a body. It is denoted using Greek letter, (Î¼).

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