A lever is a simple machine that contains a bar that can turn around a fixed point called a fulcrum. Levers change the direction, distance, or size of the applied force and make work easier. There are three classes of levers based on the position of the fulcrum, effort force, and resistance force. A first-class lever has the fulcrum between the effort and resistance, like a screwdriver. A second-class lever has the resistance between the effort and fulcrum, like a wheelbarrow. A third-class lever has the effort between the fulcrum and resistance, like a broom.

1. WORK AND MACHINES
CHAPTER 8

2. LESSON 4: USING LEVERS
 A screwdriver, used to pry the lid from a can, is an
example of a simple machine.
 A simple machine is a tool with few parts that
makes it easier or possible to do work.
 Simple machines change the
direction, distance, or size of the force you
apply.

3. THE LEVER
 A lever is a simple machine containing a bar
that can turn around a fixed point.
 The fixed point of a lever is called a fulcrum.
 Levers can have many shapes.

4.  In the figure, a person is using a lever to move a
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boulder; as the person pushes down, the boulder
moves up.
The force the person applies to the machine is called
effort force.
The object to be lifted, the boulder, is called the
resistance.
The force the machine uses to move the resistance is
called the resistance force.
The force the machine exerts is greater than the
force the person exerts, SO using a machine makes

5. THE THREE CLASSES OF
LEVERS
 Levers can be grouped into three classes.
 The classes of levers are based on the position
of the resistance force, the fulcrum, and the
effort force.
 In a first-class lever, the fulcrum is positioned
between the effort and the resistance.
 Using a screwdriver to open a paint can is an
example of a first-class lever.

6.  In a second-class lever, the resistance is
positioned between the effort and the fulcrum.
 Wheelbarrows, paper cutters, and most
nutcrackers are examples of second-class levers.

7.  In a third-class lever, the effort is positioned
between the fulcrum and the resistance.
 A broom is an example of a third-class lever.