Unit One :- Force and Motion
Lesson One: - Types of levers
1- Pliers, Crowbar, Bottle opener and others are simple machines that
are called levers
2- Machines are different in shape and size- they consist of a rigid bar
(straight or curved)- are made of different substances- are used in
moving an object which produces resistance- there must be a person
to inflict force on each instrument-there is a fixed point on which the
bar rotates and is called fulcrum- the simple machines are called
levers
3- Lever :- is a rigid bar that rotates around a fixed point called
fulcrum and is also affected by force and resistance
4- Importance (Functions) of Levers:1- Increasing force such as Crowbar and Nutcracker
The Crowbar : saves the effort exerted by using small force to move a
heavy load
2-Increasing distance such as Manual broom
In the manual broom, the hand moves a small distance from the top
while the bottom part moves a longer distance. Hence , some levers
allow exerting force through a small distance to make the resistance
arm moves for a longer distance
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3- Transferring force from one place to another such as Manual
broom
The manual broom is also used to move the force of the hand
downwards without bending the body to collect the garbage
4- Increasing speed such as the hockey bat
The hockey bat increases the speed of the ball when hitting it .Hence,
some levers increase the speed of the objects they inflict on
5- Accuracy in performance such as tweezers
The tweezers are used in picking minute objects
6- Avoiding dangers such as coal holder, ice holder and the poisonous
chemical substances holders
The coal holder picks up the coal so it protects man from heat . The
ice holder ,as well , protects man against cold and also the tweezers of
solid poisonous chemicals
Types of Levers :Levers are divided into three types according to the location of force ,
resistance and fulcrum
In the first class Levers ,the fulcrum (O) lies between force (F) and
resistance ( R)
Such as :- the scissors , the see-saw swing , the crowbar , the pliers
and hand-powered water pump
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In the second class levers , the resistance ( R ) lies between force
( F ) and fulcrum ( O)
Such as :- the nutcracker , the bottle opener , the wheel barrow
In the third class levers: - the force (F) lies between resistance (R)
and fulcrum (O)
Such as: - fishing rod, sweet holder, manual broom and ice holder
Give reason for: - Manual broom is a third class lever
Because the force lies between resistance and fulcrum
Questions to Lesson One
Question One :- Complete the following sentences :
1- A simple machine that is composed of a bar and makes jobs done
easier is called …………..
2- The crowbar is a ……………………class lever , while ………….is a third
class lever
3- The manual broom is a …………….class lever, while the scissors is
a …………………class lever
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4- In third class lever, the …………….lies between …………….and ……………
5- Among the functions of lever is to avoid…………….as in…………………
6- levers make the job easier to do through ……………..and …………………
7- Scissors and see-saw swing are ………….class levers
8- The lever is a rigid bar that rotates around a fixed point called ………
And is also affected by ……………………and………………….
9- The nutcracker is a ……………………..class…………
10- Levers which make tasks perform more easily by means of
…………….,………………….or………………..
11- The type of the lever where the arm of the force and the arm of
the resistance are equal is ………………
Question Two , Give reason for ;
1-The sweet holder is a third class lever
………………………………………………………………………………………………………..
………………………………………………………………………………………………………
2- Some levers have great importance to our lives
…………………………………………………………………………………………………………
………………………………………………………………………………………………………..
3-The see-saw swing is a first class lever
………………………………………………………………………………………………….
………………………………………………………………………………………………….
Question Three , Mention one function for each the following :
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1- Coal holder ……………………………………………………………………...
2- Crowbar……………………………………………………………………………
3- Hockey bat …………………………………………………………………….
4- Manual broom ……………………………………………………………….
Question Four, Write the scientific term of the following :
1- Levers that have the fixed point between the force and the
resistance
(…………………………………..)
2- Levers that have the force between the fixed point and resistance
(…………………………………….)
3- A rigid bar, straight or curved , rotates around a fixed point called
fulcrum and is affected by force and resistance (…………………………….)
Question Five, Define each of the following:
1- Lever …………………………………………………………………………………………….
2- Fulcrum ………………………………………………………………………………………..
3- First class lever ……………………………………………………………………………..
4- Second class lever ………………………………………………………………………….
5- Third class lever …………………………………………………………………………..
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