# Kinetic Friction, Details About Kinetic Friction, Types of Friction (For CBSE, ICSE, IAS, NET, NRA 2022)

Get unlimited access to the best preparation resource for competitive exams : get questions, notes, tests, video lectures and more- for all subjects of your exam.

# Kinetic Friction

• It is the Resistance of a Surface to an Object the Instant It Starts Moving.
• When Two Surfaces Are Moving with Respect to One Another, the Frictional Resistance is Almost Constant over a Wide Range of Low Speeds, and in The Standard Model of Friction the Frictional Force is Described by the Relationship below.
• The Coefficient is Typically Less Than the Coefficient of Static Friction, Reflecting the Common Experience That It is Easier to Keep Something in Motion Across a Horizontal Surface Than to Start It in Motion from Rest.

• Definition: A force that acts between moving surfaces. A body moving on the surface experiences a force in the opposite direction of its movement. The magnitude of the force will depend on the coefficient of kinetic friction between the two materials.
• Friction is defined as the force that holds back a sliding object.
• The kinetic friction is a part of everything and it interferes motion of two or more objects.
• The force acts in the opposite direction to the way an object wants to slide.
• If a Bus has to stop, we apply brakes and that is exactly where the friction comes into play.
• But when we have to stop in the middle of a puddle, things get harder since friction is less there and cannot aid one so much.

## Kinetic Friction Formula

• The coefficient of kinetic friction is denoted by the Greek letter μ, with a subscript “k.”
• The force of kinetic friction is times the normal force on a body.
• It is expressed in Newtons (N) .
• The kinetic friction equation can be written as:
• Force of kinetic friction = (coefficient of kinetic friction) (normal force)

Where,

• = force of kinetic friction
• = coefficient of kinetic friction
• = normal force (Greek letter “eta” )

## Types of Friction

• Static Friction
• Kinetic Friction

### Static Friction

• It is the one present between two objects that are not moving with respect to each other.
• In liquids, friction is the resistance between moving layers of a fluid better known as viscosity.

### Kinetic Friction

• Now take two moving solid objects, this is known as moving or kinetic friction due to its motion.
• It is a particular fraction of the perpendicular force acting between two bodies.
• A coefficient of friction determines the fraction which in turns determined through experiments.
• The force is independent of the contact area and doesn՚t change no matter how fast the two objects are moving. In other scenario, static friction is what affects stationary objects.
• The force of friction is a force that resists motion when two objects are in contact.

## Applications of Kinetic Friction

• It plays a huge role in everyday occurrences like while rubbing of two objects takes place. The resulting motion converts into heat and thus resulting in the fire in some instances.
• For wear and tear and that՚s why we need oil to lubricate machine parts, as it reduces friction.