Ever wondered what makes it easy to walk on the floor or how is it possible to write on a board without any problem? The answer for all such questions is friction. There exists a force between two surfaces that are in contact which makes all these things possible. Let’s understand more about friction.

**What is friction?**

Friction is defined as the force which is responsible for the sliding of an object over the other. Example of friction is pushing a bicycle over the floor. Friction always works in the opposite direction.

**Laws of friction**

There are five laws of friction and they are as follows:

- Friction is dependent on the nature of the surfaces that are in contact.
- Kinetic energy of the object is independent of the object’s velocity.
- The coefficient of kinetic friction is less than the coefficient of static friction.
- Friction is independent of the area of surfaces that are in contact.
- The frictional force and normal force are perpendicular to each other and therefore, friction is directly proportional to the normal force.

**Types of friction**

There are five types of frictions and they are as follows:

- Static Friction
- Rolling friction
- Kinetic Friction
- Sliding Friction
- Fluid Friction

**Static Friction**

Static friction is defined as **types of friction** which occurs when the surfaces are in contact at rest. Examples of static friction are book resting on the table and coffee mug resting on the study table. The coefficient of static friction is given as follows:

*f _{s } = F_{N } . μ_{s} *

Where,

f_{s} is the static friction

F_{N} is the normal force

μ_{s} is the coefficient of static friction

**Rolling friction**

Rolling friction is defined as a type of friction which resists the motion of wheel or ball. Examples of rolling friction are wheels of the moving vehicles and rolling the ball on the floor. Rolling friction is the weakest friction of all. The coefficient of rolling friction is given as:

*f _{r } = F_{N } . μ_{r} *

Where,

f_{r} is the rolling friction

F_{N} is the normal force

μ_{r} is the coefficient of rolling friction

**Kinetic Friction**

Kinetic friction is defined as a type of friction which acts between moving surfaces. When an object is moved, it experiences a force in the opposite direction. Pulling a heavy log of wood is an example of kinetic friction as there is a force acting on it in the opposite direction. The coefficient of kinetic friction is given as:

*f _{k } = F_{N } . μ_{k} *

Where,

f_{k} is the kinetic friction

F_{N} is the normal force

μ_{k} is the coefficient of kinetic friction

**Sliding Friction**

Sliding friction is defined as a type of friction which creates a resistance between two objects when they are slid against each other. Examples of sliding friction are two cards being slid over each other and sliding of the box across the floor. The coefficient of sliding friction is given as:

*f _{s } = F_{N } . μ_{s} *

Where,

f_{s} is the sliding friction

F_{N} is the normal force

μ_{s} is the coefficient of sliding friction

**Fluid Friction**

Fluid friction is a type of friction which is defined as the friction that exists between the layers of the fluid. Swimming is an example of fluid friction.

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