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Chapter 12
Section 2 Simple Machines
Objectives
• Name and describe the six types of simple machines.
• Discuss the mechanical advantage of different types
of simple machines.
• Recognize simple machines within compound
machines.
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Chapter 12
Section 2 Simple Machines
Bellringer
You may not think of a
door as a simple machine,
but it is one. It functions
like a lever. Like other
levers, when you exert a
force on it (an input force),
a force is exerted along
the entire door (the output
force).
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Chapter 12
Section 2 Simple Machines
Bellringer, continued
1. For all levers, one point along the lever stays still
while the rest of the lever moves. This point is called the
fulcrum. Where is the fulcrum of a door?
2. You can push at any point along the width of a door
and it will open. Which position requires the least force:
pushing the door near the hinges, in the middle, or near
the side farthest from the hinges? (Hint: Which of these
feels easiest to do?)
3. If you are trying to prop the door open, but your only
doorstop is not very heavy, is it likely to work best near
the hinges, in the middle, or near the side farthest from
the hinges?
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Chapter 12
Section 2 Simple Machines
The Lever Family
• The most basic machines are called simple
machines.
• The six types of simple machines are divided into two
families.
The lever family:
The inclined plane family:
• simple lever
• simple inclined plane
• pulley
• wedge
• wheel and axle
• screw
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Chapter 12
Section 2 Simple Machines
The Lever Family, continued
• Levers have a rigid arm and a fulcrum.
• Levers are divided into three classes.
• All first-class levers have a fulcrum located
between the points of application of the input and
output forces.
• In a second-class lever, the fulcrum is at one end
of the arm and the input force is applied to the
other end.
• Third-class levers multiply distance rather than
force. As a result, they have a mechanical
advantage of less than 1.
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Chapter 12
Section 2 Simple Machines
Levers
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Chapter 12
Section 2 Simple Machines
Lever
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Chapter 12
Section 2 Simple Machines
The Lever Family, continued
• Pulleys are modified levers.
• The point in the middle of a pulley is like the
fulcrum of a lever.
• A single, fixed pulley has a mechanical advantage
of 1.
• Multiple pulleys are sometimes put together in a
single unit called a block and tackle.
• A wheel and axle is a lever or pulley connected to a
shaft.
• The steering wheel of a car, screwdrivers, and
cranks are common wheel-and-axel machines.
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Chapter 12
Section 2 Simple Machines
Pulleys
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Chapter 12
Section 2 Simple Machines
Pulley
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Chapter 12
Section 2 Simple Machines
The Inclined Plane Family
• Inclined planes multiply and redirect force.
• An inclined plane turns a small input force into a
large output force by spreading the work out over
a large distance.
• A wedge is a modified inclined plane.
• A screw is an inclined plane wrapped around a
cylinder.
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Chapter 12
Section 2 Simple Machines
Inclined Plane
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Chapter 12
Section 2 Simple Machines
Screws
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Chapter 12
Section 2 Simple Machines
Compound Machines
• A machine made of more than one simple machine is
called a compound machine.
• Examples of compound machines are:
• scissors, which use two first class levers joined at
a common fulcrum
• a car jack, which uses a lever in combination with
a large screw
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