Watch the following video, and answer the

questions

What is the lever?

How many classes of levers are there?

Module objectives After the completion of this module, you will be able to

• Identify levers.

• Calculate the mechanical advantage of a lever.

• Calculate forces and lengths related to levers

• Distinguish and explain the differences between the three classes of levers

• Give real examples of the different types of levers

Introduction to levers

Introduction to levers

In The previous module you have studied the different types of simple machines, lever is one of the most commonly used simple machines.

But, What is a lever?

Definition of lever

A lever is a rigid bar that is used to transfer force.

With a pivot or sometimes called fulcrum, the lever can be used to change force that is applied (effort) by changing the position of the pivot along the lever..

Feature of leversEFFORT, PIVOT (fulcrum), and LOAD are the three features that are common in every levers.

• Pivot: is the point on which the lever balances (or fulcrum)

• Load is the weight or resistance that needs to be overcome.

• Effort is the force you apply to the lever.

Feature of levers

Of Levers

What is the Mechanical advantage

Mechanical advantage

The mechanical advantage of a machine is the ratio of the output force produced by a machine to the applied input force.

Mechanical advantage of lever

In levers, the ideal mechanical advantage (MAi) of a lever is the ratio of the length of the effort arm (LE) to the length of the load arm (LL).

Mechanical advantage of lever

It can be calculated using the following formula:

The amount of effort in leversThe amount of effort needed to lift a given load with any lever can be calculated using the formula:

Page4

Example 1

Example 1

Refer to the figure, calculate the following :

1. The effort needed to balance the 400 N, given that the load arm length is 2m .

2. The ideal mechanical advantage.

Example 1 solution1. The effort is calculated as follows

FE x LE = FL x LL

FE x 2m = 400 N x 0.4 m

FE = 400 N x 0.4 m / 2 m

FE = 80 N

Example 1 solution1. The mechanical advantage is calculated as follows :

MAi= LE / LL

MAi = 2 m / 0.4 m

= 5

Example 3 :

• Find the amount of load

• Calculate the mechanical advantage

Note that

Now Try to solve this

example

Example 2:

• Find the amount of effort

• Calculate the mechanical advantage

Example 2 solution1. The effort is calculated as follows

FE x LE = FL x LL

FE x 2.5m = 250 N x 1m

FE = 250 N x 1m / 2.5 m

FE = 100 N

Example 2 solution1. The mechanical advantage is calculated as follows :

MAi= LE / LL

MAi = 2.5 m / 1m

=2.5

Note that

The mechanical advantage = 2.5 , this means that the Amount of effort (FE) is less than the amount of load (FL) by 2.5 times, and the effort arm length (LE) is greater than the load arm length(LL) by 2.5 times

Example 3 solution1. The effort is calculated as follows

FE x LE = FL x LL

800 x 4 m= FL x 2 m

FL = 800 N x 4m / 2 m

FL = 1600 N

Example 3 solution1. The mechanical advantage is calculated as follows :

MAi= LE / LL

MAi = 4 m / 2 m

= 2

Note that

The mechanical advantage = 2 , this means that the Amount of effort (FE) is less than the amount of load (FL) by 2 times, and the effort arm length (LE) is greater than the load arm length(LL) by 2 times

Example 4 :

• Find the amount of effort

• Calculate the mechanical advantage

Example 4 solution1. The effort is calculated as follows

FE x LE = FL x LL

FE x 2 m= 500 x 5 m

FL = 500 N x 5m / 2 m

FL = 1250 N

Example 4 solution1. The mechanical advantage is calculated as follows :

MAi= LE / LL

MAi = 2 m / 5 m

=0.4

Note that

The mechanical advantage = 0.4, which is less than 1, in this case, the effort force is more than the load force, because the effort arm length is more than the load arm length.

Example 5 :

• Find the amount of effort

• Calculate the mechanical advantage

Example 5 solution1. The effort is calculated as follows

FE x LE = FL x LL

FE x 7 m= 350 x 2.5 m

FL = 350 N x 2.5m / 7 m

FL = 125 N

Example 5 solution1. The mechanical advantage is calculated as follows :

MAi= LE / LL

MAi = 7 m / 2.5 m

=2.8

Note that

The mechanical advantage = 2.8 , this means that the Amount of effort (FE) is less than the amount of load (FL) by 2.8 times, and the effort arm length (LE) is greater than the load arm length(LL) by 2.8 times

Example 6

!

• Calculate the ideal mechanical advantage

Effort =50 NLoad =300 N

LE =??LL =1

Example 6 solution1. The effort is calculated as follows

FE x LE = FL x LL

50 x LE = 300 x 1 m

LE = 300 N x 1m / 50 N

LE = 6 m

Example 6 solution1. The mechanical advantage is calculated as follows :

MAi= LE / LL

MAi = 6 m / 1 m

=6

Note that

The mechanical advantage = 6 , this means that the Amount of effort (FE) is less than the amount of load (FL) by 6 times, and the effort arm length (LE) is greater than the load arm length(LL) by 6 times

Try to solve the question page 6

Quick class activityMaitha was given the task of moving a table of 600 N, where the load arm length is 5 m and the effort arm length is 10 m.

• Calculate the effort needed

• Calculate the ideal mechanical advantage.

Answer to question 1. The effort is calculated as follows

FE x LE = FL x LL

FE x 10 m = 600 x 5 m

FE = 600 N x 5m / 10 N

FE = 300 N

1. The mechanical advantage is calculated as follows :

MAi= LE / LL

MAi = 10 m / 5 m

=2

Answer to question

Note that

The mechanical advantage = 2 , this means that the Amount of effort (FE) is less than the amount of load (FL) by 2 times, and the effort arm length (LE) is greater than the load arm length(LL) by 2 times

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Classes of levers

Watch the following video

What are the main feature of levers?

How many classes of levers are there?

Classes of levers

There are three classes of levers:

• First class

• Second class

• Third class

First class lever

First class leverFirst class lever have the fulcrum (pivot) positioned between the effort and the load.

See-saw game is an example of a first class lever.

Can you think of another example??

Second class lever

Second class leverIn the second class lever, the load is positioned between the fulcrum (pivot) and the effort.

Nut cracker is a second class lever.

Third class lever

Third class leverThird class levers have the effort positioned in the middle between the load and pivot

Tweezers are typical example of third class levers.

The following pictures are examples of third class levers.

Class activityWatch the hammer video and determine which class of lever it is.

Identify the pivot, the load, And the effort.

First class lever

PivotLoad

Effort

Class activityWatch the can crusher video, and determine which class of lever it is.

Identify the pivot, the load, And the effort.

Second class lever

Pivot

Load

Effort

Class activityRefer to the scissors image shown, and determine which class of lever it is.

Identify the pivot, the load, And the effort.

First class lever

PivotLoad

Effort

Class activityRefer to the wheel barrow image shown, and determine which class of lever it is.

Identify the pivot, the load, And the effort.

Second class leverPivot

Load

Effort

Class activityRefer to the fishing rod image shown, and determine which class of lever it is.

Identify the pivot, the load, And the effort.

Third class lever

Pivot

Load

Effort

Class activityRefer to the shovel image shown, and determine which class of lever it is.

Identify the pivot, the load, And the effort.

Third class lever

Pivot Load

Effort

At these examples and decide what class of lever there is

Study the given tools given to you by the teacher,

• Identify the effort, pivot, and fulcrum

• decide which class of levers there?

class activity 2:

Did you know?

Human body contains different classes of levers.

Can you give an example?

Did you know that?

Practical tasks

Task 1• Determine which class of lever is this?

• Identify the pivot, the load, and the effort.

• Calculate the mechanical advantage.

EffortLoad

Pivot

First class

Task 2• Determine which class of lever is this?

• Identify the pivot, the load, and the effort.

• Calculate the mechanical advantage.

Effort

Load Pivot

Second class

Task 3• Determine which class of lever is this?

• Identify the pivot, the load, and the effort.

• Calculate the mechanical advantage.

EffortLoad

Pivot

Third class

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