FRICTION

WHAT IS FRICTION?

Friction is a catchall word that refers to any force that resists relative tangential motion (or intended motion). "Relative tangential motion" is a fancy way to say "slipping" or "sliding". Its direction is opposite the relative velocity (or intended velocity). Therefore, friction is defined as a force which opposes the relative motion between two or more surfaces that are contact.

TYPES OF FRICTION?

There are four types of friction: static, sliding, rolling, and fluid friction. Static, sliding, and rolling friction occur between solid surfaces. Static friction is strongest, followed by sliding friction, and then rolling friction, which is weakest. Fluid friction occurs in fluids, which are liquids or gases.

NOTE: SLIDING FRICTION, ROLLING FRICTION AND FLUID FRICTION ARE TYPES OF DYNAMIC FRICTION. 

STATIC FRICTION

Static friction exists between a stationary object and the surface on which it is resting. It prevents an object from moving against the surface.

Examples: static friction prevents an object like book falling from the desk even if the desk is slightly tilted, it helps us to pick up an object without slipping through our fingers.

When we want to move an object first we must overcome the static friction acting between the object and the surface on which the object is resting.

A stationary book on surface

SLIDING FRICTION

Sliding friction occurs between objects as the slide against each other. It acts in the direction opposite to the direction of motion. It prevents the object from moving too fast. It is also called as kinetic friction.

Examples: A book sliding from an inclined desk, A kid sliding on a slide.

When sliding friction is acting there must be another force existing to keep the body in moving, in case of the book sliding from the desk the other force acting is gravitational force.

children sliding on a slide

ROLLING FRICTION

Rolling friction hinders the motion of an object rolling on a surface, that means it slows down the motion of an object rolling on a surface.

Examples: It slows down a ball rolling on a surface and it slows down the motion of tire rolling on the surface.

Like sliding friction here also another force is required to keep the object in motion, in case of pedaling bicycle the bicyclist provides the force which is required for the bicycle to be in motion.

A ball rolling on a surface

FLUID FRICTION

Fluid friction is experienced by the objects moving through a fluid.Fluid friction acts between the object and the fluid through which it is moving.It is also called as drag.This force depends upon the object's shape, material, speed with which it is moving and the viscosity of the fluid. Viscosity is the measure of resistance of the fluid to flow and it differs from one fluid to other.

Examples: It slow downs the motion of airplane flying in the air, here the airplanes engine helps the plane to overcome the fluid friction and move forward.

A plane in air

NOTE: SLIDING FRICTION, ROLLING FRICTION AND FLUID FRICTION ARE TYPES OF DYNAMIC FRICTION. 

LAWS OF FRICTION

THE FIVE LAWS OF FRICTION 

1. When an object is moving, the friction is proportional and perpendicular to the normal force (N)

2. Friction is independent of the area of contact so long as there is an area of contact.

3. The coefficient of static friction is slightly greater than the coefficient of kinetic friction.

4. Within rather large limits, kinetic friction is independent of velocity.

5. Friction depends upon the nature of the surfaces in contact.

6. Friction is the force which opposes the relative motion between two or more surfaces that are contact

7. The ratio of the limiting frictional force is and the normal reaction equals a constant which is known as the co-efficient of static friction

ADVANTAGES OF FRICTION       

Friction plays a vital role in our daily life. Without friction we are handicap.

1. It is becomes difficult to walk on a slippery road due to low friction. When we move on ice, it becomes difficult to walk due to low friction of ice.

2. We cannot fix nail in the wood or wall if there is no friction. It is friction which holds the nail.

3. A horse cannot pull a cart unless friction furnishes him a secure Foothold.

DISADVANTAGES OF FRICTION  

Despite the fact that the friction is very important in our daily life, it also has some disadvantages like:

1. The main disadvantage of friction is that it produces heat in various parts of machines. In this way some useful energy is wasted as heat energy.

2. Due to friction we have to exert more power in machines.

3. It opposes the motion.

4. Due to friction, noise is also produced in machines.

5. Due to friction, engines of automobiles consume more fuel which is a money loss.

METHODS OF REDUCING FRICTION

There are a number of methods to reduce friction in which some are discussed here.

1. USE OF LUBRICANTS:

The parts of machines which are moving over one another must be properly lubricated by using oils and lubricants of suitable viscosity.

2. USE OF GREASE:

Proper greasing between the sliding parts of machine reduces the friction.

3. USE OF BALL BEARING:

In machines where possible, sliding friction can be replaced by rolling friction by using ball bearings.

4. DESIGN MODIFICATION:

Friction can be reduced by changing the design of fast moving objects. The front of vehicles and airplanes made oblong to minimize friction.