Friction is the force that resists the relative movement of solid surfaces, fluid layers, and material elements sliding against each other.
CONTENT
A) FORCE
DEFINITION OF FORCE
TYPES
B) FRICTION
DEFINITION OF FRICTION
TYPES OF FRICTION
COEFFICIENT OF FRICTION
ADVANTAGES AND DISADVANTAGES OF FRICTION
WAYS OF REDUCING FRICTION
DEFINITION OF FORCE
In physics, force is any effect that, when not opposed, changes the movement of an object. It can cause an object with mass to change its speed(including moving from a stationary state), i.e. acceleration. It can also be intuitively described as pushing or pulling and has size and direction, making it a vector quantity. IT MEASURES IN SI UNITS OF NEWTON (N). The symbol is represented as F
F = Mass x Acceleration
Force is a physical cause that can change the state of motion or the dimensions of an object. There are two types based on their applications:
- Contact Force
- Non-Contact Force
Contact Force
They that act on a body either directly or through a medium are called contact forces.
Some examples are:
- Muscular
- Mechanical
- Frictional

Contact force
Non-Contact Force
Forces that act through spaces without making direct contact with the body are called non-contact forces.
Examples of non-contact forces are:
- Gravitational
- Electrostatic
- Magnetic

Non contact force
FRICTION
Friction is defined as the resistance provided by the surfaces in contact when they move with each other.
TYPES OF FRICTION
There are four types of friction and they are classified as follows:
- Static friction
- Sliding friction
- Rolling friction
- Fluid friction
All four types of frictions are different from each other.

Friction acting on a block being pulled on a surface
STATIC FRICTION: Static friction is defined as the friction force acting on the surface relative to each other when the surface is stationary. When a small amount of force is applied, the size of the static force is equal in the opposite direction. When the force increases, the maximum static friction is reached at some point.
Following are the examples of static friction:
- Creating heat by rubbing both the hands together
- Table lamp resting on the table
KINETIC FRICTION: Kinetic friction is defined as the resistance that is created between any two objects when they are sliding against each other. Following are some examples:
- Sliding of the block across the floor
- Two cards sliding against each other in a deck
ROLLING FRICTION: Rolling friction is defined as the force which resists the motion of a ball or wheel and is the weakest types of friction. Following are the examples of rolling friction:
- Rolling of the log on the ground
- Wheels of the moving vehicles
FLUID FRICTION: Fluid friction is defined as the friction that exists between the layers of the fluid when they are moving relative to each other. Following are the examples of fluid friction:
- The flow of ink in pens
- Swimming
COEFFICIENT OF FRICTION
The coefficient of friction (COF), usually represented by the Greek letter μ, is a dimensionless scalar value that describes the ratio of the friction between two objects to the force that presses them together. The coefficient of friction depends on the material used; for example, ice on steel has a low coefficient of friction, while rubber on the road has a high coefficient of friction. The coefficient of friction ranges from close to zero to greater than one.
For surfaces at rest relative to each other µ = µs where µs is the coefficient of static friction.
For surfaces in relative motionµ = µk, where µk is the coefficient of kinetic friction.
ADVANTAGES
It helps us to stop and walk
It helps for the transfer of energy
It helps to start a fire
It helps to hold unto surfaces
DISADVANTAGES
It produces unwanted heat
It reduces efficiency of machines
It causes wear and tear
It produces unwanted noise
WAYS OF REDUCING FRICTION
- Make surfaces smooth by grinding.
- Lubrication
- Streamlined body
- Reduce pressure or weight on the object.
- Reduce contact between surfaces by electrostatic magnetic levitation etc.
- Use rolling friction instead of sliding friction.
- Use fluid friction instead of the dry friction.