Transcript Grade 8 Unit 4 Mechanical Systems Topic1 Prange

Grade 8 Unit 4 Mechanical
Systems
Topic 1: Levers and Inclined Planes
Lever
A lever is a simple machine that changes the
amount of force you must exert in order to
move an object. A lever consists of a bar that is
free to rotate around a fixed point known as
the fulcrum.
Lever
Fulcrum
Lever
The fulcrum is the point of the lever that does
not move; the lever’s point of rotation.
The fulcrum supports the lever.
Lever
The effort force is the force applied on a lever to
make it move.
The term “effort force” is also used to describe
the force supplied to any machine in order to
produce an action.
Lever
The load is the mass of an object that is moved
or lifted by a machine. The load is also the
resistance to movement that a machine must
overcome.
Lever
The effort arm is the distance between the
fulcrum and the effort force.
In a similar fashion, the load arm is the distance
between the fulcrum and the load.
Levers
Levers are sorted into three classes. The class a
lever belongs to depends on the position of the
effort force (E), fulcrum (F) or load (L).
Levers are classified by whichever of theses
three factors is in the middle.
Effort
Effort
Effort
Class 1 Lever
In a Class 1 lever, the fulcrum (F) is in the
middle.
Its advantage is that it can be used for power or
precision (it also changes direction of the
force). An example is a pair of scissors.
Class 2 Lever
In a Class 2 lever, the load (L) is in the middle.
Its advantage is that it increases the effort force
on the load. An example is a wheelbarrow.
Class 3 Lever
In a Class 3 lever, the effort (E) is in the middle.
Its advantage is that the load can be moved very
quickly. An example is a hockey stick.
Lever ID
E
L
F
Class 1 lever
Lever ID
F
E
L
Class 3 lever
Lever ID
E
F
L
Class 2 lever
Lever ID
F
E
L
Class 3 lever
Lever ID
E
F
L
Class 1 lever
Lever ID
L
F
Class 2 lever
E
Lever ID
E
F
L
Class 1 lever
Lever ID
F
L
E
Class 3 lever
Lever ID
E
L
F
Class 3 lever
Lever ID
For most people the class that is the hardest to
classify is Class 3, because it is difficult to
determine where the effort force (E) is.
Bones and Muscles: Built-in Levers
In the human body, the bones act as levers and
your joints acts as a fulcrum. Your tendons and
muscles exert the effort force on the bone. The
load might be something you are lifting or
pulling or your own body.
Bones and Muscles: Built-in Levers
Most of the levers in your body are class 3, but
the other types of levers are observable as
well.
The head and neck form a
class 1 lever.
Bones and Muscles: Built-in Levers
The flexing of the foot illustrates a class 2 lever.
E
L
F
Bones and Muscles: Built-in Levers
The arm illustrates a class 3 lever.
L
E
F
Bones and Muscles: Built-in Levers
The tip-toe maneuver illustrates a class 2 lever.
E
L
F
Bones and Muscles: Built-in Levers
The arm-lifting maneuver illustrates a class 2
lever.
L
E
F
Bones and Muscles: Built-in Levers
The arm-pulling maneuver illustrates a class 1
lever.
E
F
L
Bones and Muscles: Built-in Levers
Bones and Muscles: Built-in Levers
An Arm in Space
Levers were used in the Space
Shuttle Program and on the
International Space Station in
the form of the Remote
Manipulator System. It is
better known as the Canadarm.
It received that name because it
was made in Canada and it
works like an arm.
An Arm in Space
It is 15 m long and 38 cm in diameter. While its
own mass is 450 kg, it can deploy payloads up
to 266 tonnes in space. On the Earth, it cannot
lift its own weight. It has joints that resemble
the shoulder, elbow and wrist of a person.
An Arm in Space
The Canadarm was a valuable addition to the
space shuttle program because it helped to
launch and recover satellites and to help with
repairs of objects in space.
Although the Space
Shuttle program is
now finished, the
Candarm is still in
use in space.
An Arm in Space
Sixteen countries, including Canada, are cooperating in the planning and assembling of
the International Space Station (ISS). The
Canadarm 2 is helping construct and maintain
the ISS.
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