Simple machines
CHAPTER 10
CHAPTER 10
UNIT 10.1 Analysing lever
Simple machines
List things around them that use the principle of the lever
State what a lever can do
Identify load, force and fulcrum of the lever
Classify lever
Explain what is meant by the moment of force
Solve problems related to levers
Lever isa) A simple machine
b) Enables small effort to overcome a
heavy load
c) Can be used to lift heavy objects
d) Makes work easierA lever is a simple machine which turns
about a fixed point called the FULCRUM (F) when a force called the EFFORT (E) is applied to overcome a resisting force
known as the LOAD (L).
What is Lever ?
6 types of simple machines
Lever
WedgeWheel and
axle
Inclined plane
Pulley
Screw
Types of Simple Machines
What is Lever ?
A lever has 3 parts
a)Fulcrum (F) – the turning point or pivot
b)Effort (E) – the force applied to
overcome a resisting force called the
load
c)Load (L) – the resisting force exerted by an object
Simple MachinesE
F
L
L
E
E
F
L
L
E
L
E
E
L
FE
LF
Lever can be classified into
a) 1st class
b) 2nd class
c) 3rd class
What is Lever ?
Classes of Levers
Lever
A lever is a simple machine which turns about a fixed point called the FULCRUM (F) when a force called the EFFORT (E) is applied to overcome a resisting force known as the LOAD (L).
3 classes of levers
First class Second class Third class
First Class Lever
Relative position of F, E and L
F between E and L
Common characteristics
Common devices
• Small force is used to move a large load
• Effort moves through a longer distance than the load
• Effort is further from the fulcrum than the load
• Claw hammer
• Pliers
• Scissors
• Crowbar
E
L
F
1st class
First class lever
Second Class Lever
Relative position of F, E and L
Second class lever
L between F and E
Common characteristics
Common devices
• Small force is used to move a large load
• Effort moves through a longer distance than the load
• Effort is further from the fulcrum than the load
• Wheelbarrow
• Bottle opener
• Paper cutter
• Nutcracker
E
L
F
2nd class
Third Class Lever
Relative position of F, E and L
Third class lever
E between F and L
Common characteristics
Common devices
• Large force is used to move a small load
• Load moves through a longer distance than the effort
• Load is further from the fulcrum than the effort
• Fishing rod
• Broom
• Ice tongs
• Human arm
E
L
F
3rd class
E
L
F
1st class
E
L
F
2nd class
E
L
F
3rd class
L F E
F L E
F E L
=
=
=
EF
L
L
E
E
L
FE
LF
E
L
F
L
E
F
EL
LE
F
E
L
F
E
L
F
What is the Moment of a Force?When we loosen a bolt using a spanner, a force that is applied has
a turning effect on the spanner.
This turning effect of force is known as the moment of force
a) It is easier to loosen the bolt if you hold the spanner at position P than Q because the turning effect is greater.
b) It is also easier to loosen the bolt if a larger force is applied at P to cause a greater turning effect.
Spanner Spanner
QP
ForceForce
7 cm18 cm
What is the Moment of a Force?
• The moment of a force is the turning effect of the force
• The moment of a force is defined as:
Moment of
a force (N m)= Force (N) x Perpendicular distance from
the pivot to the force (m)
The moment of a force can be increased by
Increasing the size of the force
Applying the force at a furtherdistance from the pivot
To Calculate the Moment of a Force
Moment of
a force (N m)Perpendicular distance from the pivot to the force (m)
Opening a door
Force (N)= x
4 N
0.6 m
= 4 N x 0.6 m
= 2.4 N m
Principle of Moments in a Lever
The effort and the load produce opposing moments
Anticlockwise moment
When the lever is in EQUILIBRIUM, the sum of the anticlockwise
moments about a point is equal to the sum of the clockwise
Principle Of Moments in a Lever
When the lever system is balanced
Anticlockwise moment Clockwise moment=
Load (N) x Distance of load
from fulcrum (m)=
Effort (N) x Distance of effort
from fulcrum (m)
Moments in a Lever
Calculate the value of x using the equation below:
Answer : 18.75 cm
Load (N) x Distance of load
from fulcrum (m)
= Effort (N) x Distance of effort
from fulcrum (m)
30 cm x
250 g 400 g
CHAPTER 10
UNIT 10.1 Appreciating the innovative efforts in the design of machine
Simple machines
Devices using the principle of levers
Tongs
A spadeA hockey
stick
A crane
A fire engine
A fishing rod
Devices that Using the Principle of Levers
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