ADVANTAGES AND DISADVANTAGES OF FRICTION - METHODS OF REDUCING FRICTION

ADVANTAGES AND DISADVANTAGES OF FRICTION - METHODS OF REDUCING FRICTION

ADVANTAGES OF FRICTIONFriction 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 can not fix nail in the wood or wall if there is no friction. It is friction which holds the nail. 3. A horse can not 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 FRICTIONThere are a number of methods to reduce friction in which some are discussed here. 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. USE OF GREASE:Proper greasing between the sliding parts of machine reduces the friction. USE OF BALL BEARING:In machines where possible, sliding friction can be replaced by rolling friction by using ball bearings. 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.

NEWTON'S 2ND LAW OF MOTION

When an unbalanced force acts upon a body, it is accelerated in the direction of force. The magnitude of acceleration is directly proportional to the applied force and is inversely proportional to the mass of body.
MATHEMATICALLY
Combining (i) and (ii)
....
a = k (F)(1/m) here constant k=1
a= (1)(F)(1/m) Or
SECOND STATEMENT
With the help of above equation 2nd law of motion can be expressed as:
THE NET FORCE ACTING ON A BODY IS EQUAL TO THE PRODUCT OF THE MASS OF BODY AND THE ACCELERATION PRODUCED IN IT.
NEWTON'S 3RD LAW OF MOTION
STATEMENT:
"To every action there is a reaction equal in magnitude but opposite in direction"
OR
"When a body exerts a force on another body, the second body also exerts a force on the first body of same magnitude but in the opposite direction"
FACTION = -FREACTION
Force exerted by one body is called ACTION and the force exerted by the second body is called    REACTION.
EXAMPLES:    (1) Motion of rocket: fuel burns rapidly, exerts force in downward direction and rocket moves upward        as a reaction.    (2) Book lying on a table: weight of the book on the surface is action and the force exerted by the          surface (R) is the reaction.                         R = -W    (3) Walking on a street    (4) Motion of helicopter

FORCE & MOTION

"Force is an agent which changes or tends to change the state  of rest or of uniform motion of a body."
In the light of Newton's 2nd law of motion Force may be defined as :
"Force acting on a body is equal to the product of the mass and acceleration produced in the body."
i.e.
F = ma
Force can accelerate or decelerate a body.  Force is a vector quantity.
UNITS OF FORCE
(i) NEWTON (N) in S.I system    (ii) DYNE in C.G.S system    (iii) POUND (Lb) in BRITISH ENGINEERING SYSTEM (F.P.S)
NEWTON
Newton is the unit of force and can be defined as:
"The amount of force that produces an acceleration of 1 m/s2 in a body of mass 1-kg is equal to 1 NEWTON."
1 N = 1 kg x 1m/s2
[ N = kg m/s2]
NEWTON 'S FIRST LAW OF MOTION
STATEMENT:    Newton 's first law of motion states that:
"Every body remains at rest or continues to move with uniform velocity in straight line unless an unbalanced force acts upon it".
EXPLANATION
First law of motion consists of two parts:
PART NO 1:
The first part states that a body at rest remains at rest unless an unbalanced force acts upon it.    This part is in accordance with our common experience for example, a book lying on a table remains at    rest unless it is lifted or pushed by an external force.
PART NO 2 :
Second part states that a body in motion remains in motion with uniform velocity unless an unbalance    force acts upon it. This part is not self-evident because a ball pushed once does not continue its motion    forever. A little consideration however, shows that there is an opposing force like ground friction and air    friction acting in this case. These frictional forces are responsible to stop the ball. If we eliminate these    opposing forces, a body in motion will continue its motion forever.
INERTIA
"Tendency of a body by virtue of which the body at rest or moving with uniform velocity retains its state is called INERTIA."
OR
"Property of a body by which a body resists a force, applied to it to change its state of rest or of uniform velocity is called INERTIA."
INERTIA of a body is directly related to its mass. Heavy bodies have greater inertia while lighter bodies    have little inertia.
LAW OF INERTIA AND THE FIRST LAW OF MOTION
Every body in the universe opposes the force which tends to change its state of rest or of uniform    motion. This property INERTIA is a direct consequence of FIRST LAW OF MOTION. As heavy bodies due    to greater INERTIA requires forces of large magnitude and bodies of small masses require small forces.    By the above explanation of INERTIA we conclude that the state of rest or motion does not change by its    self unless an external force acts upon it, which is according to the FIRST LAW OF MOTION.    Thus the FIRST LAW OF MOTION is also called LAW OF INERTIA.

EQUATIONS OF MOTION EQUATIONS OF MOTION

FIRST EQUATION OF MOTION Vf = Vi + at
Consider a body initial moving with velocity "Vi". After certain interval of time "t", its velocity becomes "Vf". Now
Change in velocity = Vf - Vi  OR DV =Vf – Vi
	Due to change in velocity, an acceleration "a" is produced in the body. Acceleration is given by
	a = DV/t
	Putting the value of "DV"
	a = (Vf – Vi)/t at = Vf – Vi at + Vi =VfOR
	SECOND EQUATION OF MOTION OR S = Vit + 1/2at2
	Consider a car moving on a straight road with an initial velocity equal to ‘Vi’. After an interval of time ‘t’ its velocity becomes ‘Vf’. Now first we will determine the average velocity of body.
	Average velocity = (Initial velocity + final velocity)/2 OR Vav = (Vi + Vf)/2
	but Vf = Vi + at
	Putting the value of Vf
	Vav = (Vi + Vi + at)/2 Vav = (2Vi + at)/2    Vav = 2Vi/2 + at/2   Vav = Vi + at/2                            Vav = Vi + 1/2at.......................................(i)
	we know that
	S = Vav x t
	Putting the value of ‘Vav’
	S = [Vi + 1/2at] t
	THIRD EQUATION OF MOTION OR 2aS = Vf2 – Vi2
	Initial velocity, final velocity, acceleration, and distance are related in third equation of motion.
	Consider a body moving initially with velocity ‘Vi’. After certain interval of time its velocity becomes ‘Vf’. Due to change in velocity, acceleration ‘a’ is produced in the body. Let the body travels a distance of ‘s’ meters.  According to first equation of motion:
	Vf = Vi + at      OR Vf – Vi = atOR                          (Vf – Vi)/a = t....................(i)
	Average velocity of body is given by:
	Vav = (Initial velocity + Final velocity)/2                               Vav = (Vi + Vf)/2.................. (ii)
	we know that :
	S = Vav x t.................. (ii)
	Putting the value of Vav and t from equation (i) and (ii) in equation (iii)
	S = { (Vf + Vi)/2} { (Vf – Vi)/a} 2aS = (Vf + Vi)(Vf – Vi)
	According to [ (a+b)(a-b)=a2-b2]