1. Jaydeep Patel
School of Technology,
6

2. Machine – a tool that helps us do
work
Machines help us by:
1. Changing the amount of force on an object.
2. Changing the direction of the force.
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3. What is a Simple Machine?
A simple machine has few
or no moving parts.
Simple machines make
work easier.
Simple machine is a device
in which effort is applied
at one place and work is
done at some other place.
Simple machines are run
manually, not by electric
power.
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4. Have you ever tried to unscrew a nut, bolt,
or screw from something with your bare
hands and discovered that it was just too
tight to loosen even if you had a good grip?
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5. 6-5

6. You got the proper tool,
such as a
screw driver or wrench,
and unscrewed it!
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7. Why is it that it's so easy to
unscrew with a tool when
you can't with your bare
hands?
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8. The wrench and screw driver are
examples of a wheel and axle, where the
screw or bolt is the axle and the handle is
the wheel. The tool makes the job easier
by changing the amount of the force you
exert.
Wheel
Axle
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9. All of the simple machines can be
used for thousands of jobs from
lifting a 500-pound weight to
making a boat go. The reason why
these machines are so special is
because they make difficult tasks
much easier.
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10. What is a Compound machine?
Simple Machines can be
put together in different
ways to make complex
machinery.
If a machine, consists of many simple machines, it is called compound
machine.
Such machines are run by electric or mechanical power.
Such machines work at higher speed.
Using compound machines more work is done at less effort.
For Ex: scooter, Lathe, crane, grinding machine etc.
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11. What is a Lifting machine ?
Lifting machine is a device in
which heavy load can be lifted
by less effort.
e.g. - simple pulley
- simple screw jack
- lift
- crane. etc.
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12. Technical terms Related to Simple Machines
Mechanical advantage (MA) :
The ratio of load lifted (W) and effort required (P) is called Mechanical
advantage.
Load Lifted W
MA = ∴ MA =
Effort required P
Where, W= Load and P= Effort
Velocity ratio (VR) :
The ratio of distance moved by effort and the distance moved by load is
called velocity ratio.
Distance moved by effort y
VR = ∴ VR =
Distance moved by load x
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13. Input
Input = effort x distance moved by effort
Input = p.y
Output:
Output = load x distance moved by load
Output = W.x
• Efficiency ( η ) :
The ratio of work done by the machine and work done on the machine is called
efficiency of the machine.
output
Efficiency = × 100 %
input
Output = W . x & input = P . y
W.x W/P
∴η = × 100 = × 100
P.y y/x
MA
= × 100 %
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VR

14. Ideal machine :
A machine having 100% efficiency is called an ideal machine.
In an Ideal machine friction is zero.
For Ideal machine,
Output = input or MA=VR
Effort lost in friction (Pf):
In a simple machine, effort required to overcome the friction between
various parts of a machine is called effort lost in friction.
Let, P = effort
• effort lost in friction.
Po = effort for Ideal machine
Pf=P - Po
Pf = effort lost in friction
For Ideal machine,VR = MA
VR=W/Po
Po=W/VR
Pf = P-Po
Pf= P-(W/VR)
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15. Reversible machine :
If a machine is capable of doing some work in the reverse direction, after the
effort is removed is called reversible machine.
For reversible machine, η ≥ 50%
Non-reversible machine or self-locking machine
If a machine is not capable of doing some work in the reverse direction, after the
effort is removed, is called non-reversible machine or self-locking machine.
For non-reversible machine, η < 50%
A car resting on a screw jack does not come down on the removal of the effort.
It is an example of non-reversible machine.
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16. Condition for reversibility of machine :
W = load lifted
P = effort required
x = distance moved by load
y = distance moved by effort
P.y = input
W.x = output
Machine friction = P.y – W.x
for a machine to reverse,
output > machine friction
∴ W.x > P.y – W.x
∴ 2 W.x > p.y
W. x 1
∴ ≥
P. y 2
Output
∴ ≥ 0 .5
Input
∴ η ≥ 50%
6 - 16 For a machine to reverse, η ≥ 50%

17. Law of machine
The law of machine is given by relation,
P= mW+C
Where,
P = effort applied
W= load lifted
m = constant
(coefficient of friction)
= slope of line AB
C= Constant
= Machine Friction= OA
Following observations are made from the graph :
On a machine, if W = 0, effort C is required to run the machine. Hence, effort C is required
to overcome machine friction.
If line AB crosses x-x axis. without effort (P), some load call be lifted, which is impossible.
Hence, line AB never crosses x-x axis.
If line AB passes through origin, no effort is required to balance friction. Such a graph is for
Ideal machine.
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18. Maximum mechanical advantage
W
MA =
P
from law of machine P = mW + C
W 1 C
∴ MA = = (Q neglecting )
mW + C C W
m+
W
1
Maxi. MA =
m
Maximum efficiency (η max )
W
MA =
P
from law of machine P = mW + C
MA
∴η =
VR
1
m 1
∴η = (MA = MA max = )
VR m
1
∴ η max =
6 - 18 m x VR

19. Relation Between Load Lifted and the Mechanical Advantage
As the load increases, the effort also increases
and the M. A. increases
The maximum M. A. is equal to 1/m.
Relation Between Load Lifted and the Efficiency
As the load and effort increases, efficiency also
increases.
The maximum efficiency is equal to 1/(m x VR)
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20. Simple Machine
• Following are the simple machines.
Simple Wheel and Axle
Differential wheel and axle
Worm and Worm Wheel
Single purchase Crab
Double Purchase Crab
Simple Screw Jack
lever
Simple Pulley
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21. Simple Wheel and Axle
WHEEL AND AXLE : A wheel and
axle is a modification of a pulley.
A wheel is fixed to a shaft.
Large wheel fixed to smaller wheel (or
shaft) called an axle
Both turn together
Effort usually on larger wheel, moving
load of axle

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23. When either the wheel or axle turns,
the other part also turns. One full
revolution of either part causes one full
revolution of the other part.
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24. DIFFERENTIAL WHEEL AND AXLE
• In this machine load axle is made in two parts having two different diameters d1 and d2.
• When effort is applied to rotate the assembly at that time string is wound over larger
axle (d1) and unwound from the smaller axle (d2).
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25. WORM AND WORM WHEEL
• In worm and worm wheel machine, effort wheel and worm are on the same shaft and rotates in
two bearings as shown.
• Similarly worm wheel and load drum are also on the same shaft and rotates in two bearings. Two
axes are at right angles.
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26. CRAB WINCH
Winch crabs are lifting machines in which velocity
ratio is increased by a gear system.
If only one set of gears is used, the winch crab is
called a single purchase winch crab and if two sets
are used it is called double purchase winch crab.
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27. SINGLE PURCHASE CRAB WINCH
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28. DOUBLE PURCHASE CRAB WINCH
• In this machine to increase the V.R. one more pair of gears is used in comparison to single
purchase crab.
• Since there are totally two pairs of gears it is known as Double Purchase Crab Winch. Similarly in
Triple Purchase CrabWinch there will be three pairs of gears.
• Construction is similar in all the cases
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29. SIMPLE SCREW JACK
Screw Jack is a simple machine used for lifting heavy
loads, through short distances, with the help of small
effort applied at its handle.
The most common application of screw jack is the
raising of the front or rear portion of a vehicle for
the purpose of changing the wheel or tyre.
when one rotation is given to the handle.
distance moved by effort = 2πR
distance through which load is lifted = p
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30. LEVERS
The lever is simple machine made with a bar
free to move about a fixed point called
fulcrum.
It enables a small effort to overcome a large
load.
VR = dE/dL
6 - 30 ME = FL/FE

31. First Kind of lever
In a first Kind lever the fulcrum is in
between of load and effort.
load and effort is on either side.
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32. Second Kind of lever
In a second kind lever the fulcrum is at the
end, with the load is in between fulcrum
and effort.
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33. Third Kind of lever
In a third kind lever the fulcrum is again at
the end, but the effort is in the middle.
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34. Summary of LEVER CLASSES
1st Class 2nd Class 3rd Class
Fulcrum is between the load and Load is between fulcrum and effort •Effort is between the fulcrum and
effort load.
• Mechanical advantage • MA = b/a •MA = b/a
• MA = effort arm/load arm • MA is always greater than 1. • MA is always less than 1
MA= b/a
• MA can be more than 1,
equal to 1 or less than 1.
When MA is greater than 1, less Since. MA is always greater than 1. Since, MA is always less
effort would be required to lift a lever of second kind is an effort than 1. lever of the third
heavy load. Such type of lever is multiplier lever. kind is only a speed multiplier
called effort multiplier lever. lever. Such levers cannot lift heavy
loads but provide increase in speed
of lifting.
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35. Simple Pulley
PULLEY: A pulley is a simple machine
made with a rope, belt or chain wrapped
around a grooved wheel.
A pulley works two ways. It can change the
direction of a force or it can change the
amount of force.
A fixed pulley changes the direction of the
applied force. ( Ex. Raising the flag ) .
A movable pulley is attached to the object are
moving.
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36. Direction of Effort In Simple Pulley
Pulley can change the direction of a Effort(force).
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37. TYPES OF PULLEYS
FIXED PULLEY
(like flagpole)
Pulley stays in one position
Moves LOAD up, down or
sideways
Changes DIRECTION of force
Does not reduce EFFORT
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38. TYPES OF PULLEYS
MOVABLE PULLEY
(for lifting or lowering heavy objects)
Moves along with LOAD
Reduces EFFORT
Increases DISTANCE
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39. System OF PULLEYS
First system of pulleys
Second system of pulleys
Third system of pulleys
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40. First system of pulleys
First system of pulley : VR = 2n
Where, n = no. of moving Pulley
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41. Second system of pulleys
Second system of pulley: VR = n
Where, n =total no. of Pullies.
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42. Third system of pulleys
Third system of pulley : VR = 2n - 1
Where, n = total no. of Pullies.
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