Transcript Document

Parts of a
Lever
Effort
Load
Load Arm
Fulcrum
A lever is a simple machine used to reduce the amount of effort it would
take to lift a load or reduce the amount of effort needed to do work.
There are 3 types of levers: Class 1, Class 2, and Class 3. The effort
needed to lift a load is measured in Newtons.
F
A Class 1 Lever has its fulcrum between the effort and the load.
L
A Class 2 Lever has its load between the effort and the fulcrum.
E
A Class 3 Lever has the effort between the load and the fulcrum.
Levers Quiz
Use the following slides to quiz
yourself on how how well you
can match commonly used items
with their correct class of lever.
Click on the correct Lever classification for the tool pictured below.
Class 1
Class 2
Class3
Click on the correct Lever classification for the tool pictured below.
Class 1
Class 2
Class3
Click on the correct Lever classification for the tool pictured below.
Class 1
Class 2
Class 3
Click on the correct Lever classification for the tool pictured below.
Class 1
Class 2
Class 3
Click on the correct Lever classification for the tool pictured below.
Class 1
Class 2
Class 3
Class 1
Class 2
Class 3
Click on the correct Lever classification for the tool pictured below.
Class 1
Class 2
Class 3
Click on the correct Lever classification for the tool pictured below.
Class 1
Class 2
Class 3
Click on the correct Lever classification for the tool pictured below.
Class 1
Class 2
Class 3
Click on the correct Lever classification for the tool pictured below.
Class 1
Class 2
Class 3
Click on the correct Lever classification for the tool pictured below.
Class 1
Class 2
Class 3
Click on the correct Lever classification for the tool pictured below.
Class 1
Class 2
Class 3
Click on the correct Lever classification for the tool pictured below.
Class 1
Class 2
Class 3
Click on the correct Lever classification for the tool pictured below.
Class 1
Class 2
Class 3
You have successfully matched the common hand tools
with their correct classification of lever. Be sure to
remember: F L E
1 2 3
Levers can provide Mechanical Advantage by reducing the
effort needed to lift a load. The closer the fulcrum is to the
load, the less effort is needed to lift the load. The load does
not move a great distance.
L
E
F
Levers can be used to move loads farther if the fulcrum is placed close to the effort. In this situation
more effort is needed to lift the load, but the load will move farther than if the fulcrum was closer
to the load.
L
E
F
Single Fixed Pulley
This pulley provides the user Directional
Advantage, allowing someone to pull
down to lift the load up. Is Mechanical
Advantage provided with this system?
No, the effort needed to lift this load is equal to the weight of the load.
This is because the load is supported by only 1 rope arm. You must also pull
an amount of rope equal to the height you wish to lift the load
Single Moveable Pulley
This pulley system provides Mechanical Advantage, requiring only ½ the effort needed to lift the weight of
the load. If the load weighs 20 lbs, only 10 lbs of effort is needed to lift it. Can you tell why?
The load is supported by 2 rope arms under the pulley. Each load arm supports half the weight of the load, so
the arm pulling up uses only 10 lbs of effort to lift this load. You must pull twice as much rope as desired to lift
the load a certain height. Example: Pull 2 ft of rope for each 1 foot of height that you want to lift the load.
Single Fixed/Single Moveable Pulley
This pulley system combines the properties of their single components into a system that provides both
Mechanical and Directional Advantage.
Do you see how this happens? How much rope must you pull?
This pulley provides Directional Advantage by allowing the user to pull down to lift the load. It also provides
Mechanical Advantage by using 2 rope arms to support the load, reducing the effort needed to lift the load by ½.
In this system you pull 2 times as much rope for every unit of height that you want to lift the load.
Pulley Power!
Single-Fixed Pulleys provide or Directional Advantage. You can make use of CounterWeights in order to reduce your effort needed to lift the load. However, your effort
PLUS the the counter-weight together must be equal to or be more than the weight of
the load being lifted.
Single-Moveable Pulleys provide Mechanical Advantage. You must pull 2 times the
distance in rope that you wish to lift the load because the load is supported by 2
rope arms. You gain a Mechanical Advantage of 2 because you are using only ½ as
much effort to lift the load.
Combining Single-Fixed and Single-Moveable into Compound Pulley Systems allows
the user to gain both Mechanical and Directional Advantage. The more rope arms
supporting the load the greater the Mechanical Advantage.
An Inclined Plane is a simple machine that helps reduce the effort needed to move a load. Instead of
picking up this load and lifting it straight upwards, the load can be pushed along an elevated plane.
The user must move the load a greater distance, but the effort needed to move it will be less.

Work input is the amount of work done
on a machine.
› Input force x input distance

Work output is the amount of work
done by a machine.
› Output force x output distance
Wout = Win
Fout x Dout = Fin x Din
10N x 3m = 2N x 15m
Dout
3m
10 N
Din 15 m
Fin
Screw
Inclined Plane
Wrapped around post =
Screw
A Screw is really an Inclined Plane wrapped around a center post.
The mechanical advantage of an screw can be
calculated by dividing the circumference by the pitch of
the screw.
Pitch equals 1/ number of turns per inch.
Wedge
edge
Two Inclined Planes meeting together to create a sharp edge creates a Wedge.

The mechanical advantage of a wedge can
be found by dividing the length of either slope
(S) by the thickness (T) of the big end.
S
T

As an example, assume that the length of the
slope is 10 inches and the thickness is 4 inches.
The mechanical advantage is equal to 10/4 or 2
1/2. As with the inclined plane, the mechanical
advantage gained by using a wedge requires a
corresponding increase in distance.
Wedges can be put to use in a variety of ways. The
tips of screws, nails, and needles are wedges. Axes,
splitting mauls, and picks have wedge edges. Scissors
blades, pruning shears, and hand-held grass clippers
all have wedge shaped blades. Planers have wedge
shaped shapes for shaving wood particles. You will
find many more examples if you take a closer look at
many of the common tools used around your own
house. Wedges are just one form of Simple Machine
that helps us do work more easily.
The wheel must be fixed to the axle.
 One rotation of the wheel equals one
rotation of the axle.
 If the wheel and axle are not fixed then
you basically have a pulley system.

A doorknob
 Wheels on vehicles
 Fishing reel
 Carousel
 Screwdriver




Provides a simple way
to obtain Mechanical
Advantage.
The example to the
right shows a simple
system with an MA of
5:1.
The radius of the wheel
in this case is 5x the
radius of the axle.
As with any system
using MA, you give
something to gain
something.
 Here you are
increasing the distance
that you must turn to
achieve one rotation
of the axle, but you are
increasing torque at
the axle by the same
ratio, thus making it
“easier” to raise the
bucket.
