THE SIMPLE MACHINES

Lever

Pulley Wheel and Axle

WedgeScrewInclined Plane

MACHINES: A MACHINE IS A DEVICE THAT OVERCOMES A LARGE RESISTIVE FORCE AT A GIVEN POINT BY APPLYING A SMALL FORCE IN CONVENIENT DIRECTION AT A CONVENIENT POINT.

It works as a force multiplier.

It allows applying the force at convenient point.

It allows applying the force in convenient direction.

It is used to get the task achieved in less time.

SOME TECHNICAL TERMS: Mechanical Advantage: it is a ratio of load

to the effort. M.A.= LOAD (L) EFFORT (E)Where,Load is the resistive force exerted by the

object on which work is to be done.Effort is the force applied on the machine to

overcome the load in order to get the work done.

M.A > 1 for a good machine It is a unit less quantity.

SOME TECHNICAL TERMS: VELOCITY RATIO: It is a ratio of velocity of

effort to the velocity of the load. Where, VELOCITY OF EFFORT = d(e) / t and VELOCITY OF LOAD = d(l) / t

Therefore, we have VELOCITY RATIO = d(e) / d(l) ; Where d(e) and d(l) are the distances

moved by the effort and load in time t.Hence, velocity ratio can also be defined as

the ratio of distance moved by the effort to distance moved by the load.

SOME TECHNICAL TERMS: EFFICIENCY OF A MACHINE: It is defined as

the ration of work output to the work input.

Efficiency η = work output = WOUT / WIN

work input

work input is the work done on the machine by the effort.

Work output is the work done by the machine on the load.

It is a unit less quantity.

PRINCIPLE OF A MACHINE According to law of conservation of energy,

work output cannot be more than work input.

WIN = E × d(e) WOUT = L × d(l)

Therefore,

η = L × d (l) = L/E = M.A. E × d(e) d(e)/ d(l) V.R. M.A. = V.R × η Note: In practice, due to friction M.A. < V.R.So efficiency is always less than 1

Efficiency η = work output = WOUT / WIN

work input

LEVERS:

It is a rigid, straight or bent bar which is capable of turning about a fixed axis.

It has four components1. Rigid straight or bent bar2. Load3. Effort4. Fulcrum

LEVERS:

It works on the principle of momentsEffort × effort arm = Load × load arm

Load = Effort armEffort load arm But , M.A. = load / effortTherefore, M.A. = Effort arm Law of

Levers Load arm

TYPES OF LEVERS :

FULCRUM IS BETWEEN EFFORT AND LOADEFFORT MOVES FARTHER THAN RESISTANCE. MULTIPLIES EFFORT AND CHANGES ITS DIRECTION.

THE MECHANICAL ADVANTAGE OF A LEVER IS THE RATIO OF THE LENGTH OF THE LEVER ON THE APPLIED FORCE SIDE OF THE FULCRUM TO THE LENGTH OF THE LEVER ON THE RESISTANCE FORCE SIDE OF THE FULCRUM.

First Class Lever

FIRST CLASS LEVER.

Common examples of first-class levers include crowbars, scissors, pliers, tin snips and seesaws.

LOAD IS BETWEEN FULCRUM AND EFFORT. EFFORT MOVES FARTHER THAN RESISTANCE. MULTIPLIES EFFORT, BUT DOES NOT CHANGE ITS

DIRECTION THE MECHANICAL ADVANTAGE OF A LEVER IS THE RATIO OF THE DISTANCE FROM THE APPLIED FORCE TO THE FULCRUM TO THE DISTANCE FROM THE RESISTANCE FORCE TO THE FULCRUM.

Second Class Lever

SECOND CLASS LEVER Examples of

second-class levers include nut crackers, wheel barrows, doors, and bottle openers.

EF IS BETWEEN FULCRUM AND RF (LOAD) DOES NOT MULTIPLY FORCE RESISTANCE MOVES FARTHER THAN EFFORT. MULTIPLIES THE DISTANCE, THE EFFORT .

THE MECHANICAL ADVANTAGE OF A LEVER IS THE RATIO OF THE DISTANCE FROM THE APPLIED FORCE TO THE FULCRUM TO THE DISTANCE OF THE RESISTANCE FORCE TO THE FULCRUM

Third Class Lever

EXAMPLES OF LEVERS:

INCLINED PLACE: It is a sloping surface that works as a

simple machine. An inclined plane

is a flat surface that is higher on one end.

Inclined planes make the work of moving things easier.

INCLINED PLANES

M.A. = Load / Effort = W / W sin A

= 1/ sin ATherefore from the geometry of the figureWe have as follows,

M.A. = l/h l = slant height of inclined planeh = height of the inclined plane V.R. = d(e) /d(l)

V.R. = l/h

Hence efficiency η = M.A. / V.R. = 1

PULLEYS Pulley are wheels

and axles with a groove around the outside

A pulley needs a rope, chain or belt around the groove to make it do work

A SINGLE FIXED PULLEY : It’s mechanical

advantage is unity, it means equal amount of effort is needed to lift any load.

It’s used as it changes the direction of the effort

A SINGLE MOVABLE PULLEY:

A movable pulley rotates freely about the axis that itself changes its position.

Here the M.A. Is 2.

V.R. Is 2 hence the effeciency becomes 1.

A SINGLE MOVABLE PULLEY

A disadvantage here is that the effort which is to be applied is in upward direction which may not be convienent.

To solve this we can attach one fixed pully without changing the M.A.This arrangement is called Block and Tackle system.

COMBINATION OF PULLEY: The upper part of the

system consists a fixed pulley and the lower part consists of movable pulleys.

The no. of movable pulleys are equal or one less than the number of fixed pulleys.

GEARS Gears are toothed

wheels which interlock to form simple machines.

The tighter the joint, the less chance of slipping

Gears range in size but the important number is how many teeth a gear has.

PURPOSE OF GEARS It is used to increase or decrease the

turning effect of a machine. It means that if driving gear is

rotated certain number of rotations per second the driven gear as desired can be rotated at more or less number of rotations per second.

V.R. OF GEAR

V.R. = No. of rotations per second of the driving gear ( n A )

No. of rotations per second of the driven gear ( nB )

nA is inversly proportional to RA , similarly for nB and RB .

therefore we have, nA = RB = V.R.

nB RA

Also RB = NB ; Where N are no. of tooth in respective gears A and B

RA NA

MORE ABOUT GEARS Automobiles have four gears, and their

size keeps of decreasing from first to fourth.

During the first gear application , it produces low speed but largest torque.

And as we increase the no. of gears the speed keeps on increasing.