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

SMK Perempuan Likas

Sabah