Grade 9 Science Related Reading/Physics
Grade 9 Physics
9M.5: Levers and Moment
Simple Machines
Task 1 - Pre- Reading Activity
Try to list where you might find some of these Simple Machines around your house.
Simple
Machine
Where you might find the simple machines in the house
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Grade 9 Science Related Reading/Physics
Task 2 – Reading Activity
As you read through the
section, study the figures
of the types of machines.
Make a list of the six simple
machines in your notebook
and a sentence
describing how each works.
What Are the Six Types of Simple Machines?
All machines are made from one or more of the six
simple machines. They are the lever, the pulley, the wheel
and axle, the inclined plane, the wedge, and the screw.
They each work differently to change the size or direction
of the input force.
What Is a Lever?
A commonly used simple machine is the lever. A lever has a
bar that rotates at a fixed point, called a fulcrum. The force
Describe How does a
that is applied to the lever is the input force(effort). The object
lever do work?
that is being lifted by the lever is called the load. A lever is used
______________________
to apply a force to move a load. There are three classes of
______________________
levers. They all have a different location for the fulcrum, the
______________________
load, and the input force on the bar.
______________________
FIRST-CLASS LEVERS
______________________
In first-class levers, the fulcrum is between the input
______________________
force and the load as shown in the figure below. The
direction of the input force always changes in this type of
lever. They can also be used to increase either the force
or the distance of the work.
SECOND-CLASS LEVERS
In second-class levers, the load is between the fulcrum and the input force (effort) as shown in the
figure below. They do not change the direction of the input force. Second-class levers are often
used to increase the force of the work. You apply less force to the lever than the force it puts on
the load. This happens because the force is applied over a larger distance.
THIRD-CLASS LEVERS
In third-class levers, the input force is between the fulcrum and the load as shown in the figure
below. The direction of the input force does not change and the input force does not increase.
This means the output force is always less than the input force. Third-class levers do increase the
distance that the output force works.
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Grade 9 Science Related Reading/Physics
Why We Use Simple Machines
by Beverly S. Krueger
Simple machines really are simple but profoundly useful. They are the machines that man has used
throughout history to do jobs that are too big for him. When we think of machines, we might think
of the automobile or the printing press. Simple machines are much simpler than these machines. In
fact, most complex machines are made from many simple machines. Simple machines include the
incline plane, wedge, screw, pulley, lever, and wheel and axle. A simple machine requires energy to
work. Originally, that energy would come from the effort of man, animals, sometimes a millstream,
or the wind. Throughout man’s history his understanding of simple machines has developed and
grown. Today we harness the energy from coal, natural gas, oil, and nuclear power to provide the
energy needed to make our machines run.
A simple machine has few or no moving parts and makes work easier. When we study something
from a scientific perspective, we want to use the scientific terminology and scientific way of
organizing our ideas. When we talk about simple machines, it’s important to understand the
meaning of work. To us work can mean taking out the trash or completing math homework, people
go to work every day. But when we are talking about simple machines and work, we are talking
about something different. Work is the amount of force required to move an object a specified
distance. Force is a push or a pull that causes a change in motion of an object. That means it can be
used to start an object moving or stop an object that is already moving.
WORK = FORCE X DISTANCE
Simple machines are designed to make doing this type of work easier. Since we are looking at work
from a scientific perspective, we also need to use the scientific terms for measuring the
effectiveness of our machines on making work easier. We measure force in Newton, distance in
meters, and work in Joules. It works like this:
1 Newton of Force x 1 meter of Distance = 1 Joule of Work
1N x 1m = 1J or 1N-m = 1J
(Note: N-m is Newton-meter. When you multiply two variables expressed in different terms,
Newton and meters, you combine the terms into one Newton-meter or N-m.)
If we applied 10 Newton of force to move an object 5 meters that would equal 50 Joules of work.
10N x 5m = 50N-m = 50 J
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Grade 9 Science Related Reading/Physics
Task 3 – Post Reading Activity
Vocabulary check! – MAKE SURE YOU KNOW THE WORDS IN BOLD USE A DICTIONARY IF YOU
HAVE TO!
Words in bold
Definition
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Use a Venn Diagram to compare a first-class lever and a second-class lever.
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Grade 9 Science Related Reading/Physics
Q1: The three classes of lever are based on the location of what three features?
_________________________________________________________________________________
_________________________________________________________________________________
Q2: In a second-class lever, why must you exert input force over a greater distance?
_________________________________________________________________________________
_________________________________________________________________________________
Q3: Why is the output force always less than the input force in a third-class lever?
__________________________________________________________________________________
__________________________________________________________________________________
Q4: Where are the fulcrum, the load, and the input force located in a first-class lever, a secondclass lever, and a third-class lever? Draw diagrams
__________________________________________________________________________________
__________________________________________________________________________________
First Class Lever
Second Class Lever
Third Class Lever
Q5: Choose the best answer:
______ 1. A simple machine with a bar that pivots at a fixed point is a(n)
a. wedge.
c. knife.
b. lever.
d. screw.
______ 2. What is the fixed point on a lever called?
a. bolt
c. fulcrum
b. pivot point
d. wedge
______ 3. What do first-class levers always change the direction of?
a. input force
c. distance
b. output force
d. fulcrum
______ 4. When you use the claw end of a hammer to remove a nail, what type of
simple machine are you using?
a. wedge
c. screw
b. first-class lever
d. pulley
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Grade 9 Science Related Reading/Physics
Q6: Read the description. Then, draw a line from the dot next to each description to the
matching lever.
1. first-class lever
2. second-class lever
3. third-class lever
Q7: Calculate the work done in the picture below
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