1. A machine is a tool that is used to transfer energy from one point to another in order to do work more easily. Common types of simple machines include levers, wheels and axles, pulleys, inclined planes, screws, and wedges. 2. Key terms related to machines include load, effort, mechanical advantage, velocity ratio, work input, and work output. Mechanical advantage is the ratio of load to effort, while velocity ratio is the ratio of the velocities or displacements of effort and load. 3. Pulley systems like fixed pulleys change the direction of effort, while movable pulleys and block and tackle systems act as force multipliers by increasing the mechanical advantage. The mechanical advantage

1. EXCELLENCE CLASSES

2. Introduction
EXCELLENCE CLASSES
 Defn – A machine is used to transfer energy from
one point to another and allows us to do work
that could not otherwise be done or could not be
done easily.
 A machine can be used as :
 A force multiplier e.g Jack
 Changing the point of application of force to a
convenient point e.g bicycle chain.
 Changing the direction of force e.g Pulley.
 Multiply Speed e.g Gears

3. TYPES OF MACHINES
EXCELLENCE CLASSES
Simple
machines
Lever
Wheel
and
Axle
Pulley
Inclined
plane
Screw
Wedge

4. TERMS RELATED TO MACHINES
EXCELLENCE CLASSES
 Load (L) – The resistive or opposing force to be
overcome by a machine is called the load.
 Effort (E) - The force applied on the machine to
overcome the load is called the effort.
 Mechanical Advantage – It is defined as the ratio
of the resistance force (load L) to the effort (E).
M.A = L / E
It is the ratio of two forces hence it does not have
any unit.

5. EXCELLENCE CLASSES
 If L = E then, MA = 1 , Such machines is used
to change the direction
of force applied.
 If L > E then, MA > 1, Such machine is used
as force multiplier.
 If L < E then, MA < 1, Such machine is used
for gain in speed.
 Velocity Ratio – It is defined as the ratio velocity
of the effort to velocity of the load.
VR =vel.of effort /vel.of load. = VE / VL
OR
 It is also defined as ratio of displacement of the
effort to displacement of the load.
VR = disp.of effort / disp.of load = dE /dL

6. EXCELLENCE CLASSES
 Velocity ratio is the ratio of similar quantities
therefore it does not have any unit.
 If dL = dE then , VR=1 , Such machine can be
used to change the
direction of effort.
 If dL < dE then , VR>1 , Such a machine is
used as a force
multiplier.
 If dL > dE then , VR<1 , Such a machine is
used to obtain
gain in speed.
 Work Input – The work done on the machine by
the effort, is called the work input.

7. EXCELLENCE CLASSES
 Work Input = Effort x Displacement of point of
application of effort.
 Work Output – The work done by the machine on
the load, is called the work output.
 Work Output = Load x Displacement of point of
application of load.
 Efficiency – It is defined as the ratio of work
output the work input.
Ƞ = work output /work input
 If work output = work input then, Ƞ = 100 %
which is possible only in case of ideal machine.

8. EXCELLENCE CLASSES
 No machine is ideal or 100% efficient because of
the following reason:
1. There always exists friction between the parts
of the machine.
2. The string in a machine if any is not perfectly
elastic.
3. Different parts of the machine are not perfectly
rigid.
4. The moving parts of the machine are not
weightless.

9. RELATION BETWEEN Ƞ , MA & VR
EXCELLENCE CLASSES

10. LEVERS
EXCELLENCE CLASSES
 Defn – A lever consists of a rigid
bar, straight or bent, free to turn
on a pivot called fulcrum.
 Lever works on the principle of
moments which states “ When a
body is in equilibrium the sum of
the clockwise moments about any
point equals the sum of
anticlockwise moments about the
same points.”
 Unit used for measuring moment
of force is Nm.

11. TYPES OF LEVER
EXCELLENCE CLASSES

12. LEVERS FOUND IN HUMAN BODY
EXCELLENCE CLASSES

13. MA & VR of a Lever
By principle of moments,
Load x Load arm = Effort x Effort arm.
∴ Load / Effort = Effort arm / Load arm
But, MA = Load / Effort
∴ MA = Load / Effort = Effort arm / Load arm.
This is called law of lever. Thus MA of a lever is
equal to ratio of effort arm to load arm.
EXCELLENCE CLASSES

14. EXCELLENCE CLASSES
 For Class I lever
Effort arm may be equal to
greater than or less than load
arm. Therefore, MA & VR may be equal to
greater than or less than one.
 If EA > LA then, MA >1 & VR >1 such lever is
used as force multiplier.
Eg. Shears, crowbar, claw hammer.
 If If EA < LA then, MA <1 & VR <1 such lever is
used to obtain gain in speed as disp. of load is
greater than disp. of effort.
Eg. Scissor used to cut cloth.

15. EXCELLENCE CLASSES
 For Class II lever
 EA always > LA hence MA >1.
 For Ideal machine MA = VR,
therefore VR>1.
 Class II lever acts as force multiplier.
 For Class III lever
 EA always < LA hence MA <1.
 For Ideal machine MA = VR,
therefore VR<1.
 Class III lever acts as Speed multiplier.

16. Pulley System
EXCELLENCE CLASSES
 Defn – A pulley is a grooved wheel that can turn
readily on an axle and is supported in a frame.
 Pulley may be of the following types:
1. Single fixed pulley 2.Single movable pulley
3. A combination of movable pulleys ( Block & Tackle)

17. SINGLE FIXED PULLEY
EXCELLENCE CLASSES
 Defn – A pulley which has its axis of rotation fixed in
position is called a single fixed pulley.
 It is used to change the direction of effort.
 If the pulley is not rotating then,
E = T = L
∴ MA = L/E = T/T = 1.
Also distance moved by effort is equal
to the distance moved by the load.
∴ VR = dE/dL = 1
Also, Ƞ = MA / VR = 1 or 100%.
 This type of pulley is used to apply force in a
convenient direction.

18. SINGLE MOVABLE PULLEY
EXCELLENCE CLASSES
 Defn – A single movable pulley is one which can
change its axis of rotation i.e it can move up and
down along with load.
 In equilibrium and under ideal
conditions,
L = T+T = 2T (as load is
balanced by 2 T’s)
And E = T
∴ MA = L/E = 2T/T = 2.
If the rope is pulled through a distance 2d, the
pulley moves through a distance d. Thus, dE=2dL
∴ VR = dE/dL = 2dL/dL = 2

19. EXCELLENCE CLASSES
 Also, Ƞ = MA / VR = 2/2 = 1 or 100%.
 Such a Pulley acts as force multiplier.
 As MA =2 that means we can lift a much heavier
load by applying a smaller effort. But the effort
applied is in inconvenient direction.
 So in order to apply a smaller force to lift a
heavier load and also to apply the effort in a
convenient direction we need to have a fixed
pulley and a movable pulley
that moves along with the
load shown in as fig.

20. EXCELLENCE CLASSES
 For n movable pulleys and one fixed pulley MA
and VR are given by,
MA = 2n VR= 2n
Single fixed pulley Single movable pulley
It is fixed to a rigid support. It is not fixed to a rigid support.
Its mechanical advantage is one. Its mechanical advantage is two.
Its velocity ratio is one. Its velocity ratio is two.
The weight of pulley itself does
not affect its MA.
The weight of pulley itself reduces
its MA.
It is used to change the direction of
effort
It is used as force multiplier

21. BLOCK & TACKLE SYSTEM
EXCELLENCE CLASSES
 In this system the pulleys are arranged in two
blocks; the upper block which is fixed and the
lower block which is movable.
 The no. of pulleys in the lower block is either
equal to or less than the no. of pulleys in the
upper block.
 Fig alongside shows 3 fixed and 2
movable pulleys where the pulleys are
connected to a single rope, hence the
sum of tension in each rope balances
the applied load.
 ∴ L=T+T+T+T+T = 5T

22. EXCELLENCE CLASSES
 Also, E =T
∴ MA =L/E = 5T/T = 5