Levers - emmanueldrbbsclasses

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LEVERS
What is a lever?
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The lever is a very simple and common machine that
can be used to reduce the effort that is needed to get
a job done.
A lever is usually a long, rigid object that moves around
a turning point called a fulcrum or pivot.
You need to put in an effort to make the lever move a
load.
Levers are named according to where the fulcrum, load
and effort are positioned along the lever.
There are three types of levers:
First class levers
 Second class levers
 Third class levers
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What do levers do?
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All levers are either force multipliers or speed
multipliers.
Force multiplying levers
Multiply the effort you use.
 This means that you may be able to move loads that you
couldn’t move without the lever.
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Speed multipliers
Increase the speed of an object.
 A big effort needs to be applied, but the load moves over a
greater distance, at a higher speed.
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First-Class Levers
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First-class levers turn
around a fulcrum that is
between the effort and
the load.
First-class levers are force
multipliers.
Examples include:
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seesaw
shoehorn
wheel and axle - because
the wheel's motions follows
the fulcrum, load arm, and
effort arm principle.
chopsticks with hand - the
middle finger acts as a
pivot.
First-class levers in your body
Nod your head
 Pivot is the place where
your skull meets the top of
your spine.
 Skull is the lever arm and
the neck muscles at the
back of the skull provide
the force (effort) to lift
your head up against the
weight of the head (load).
 When the neck muscles
relax, your head nods
forward.
Second-Class Levers
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Second-class levers turn
around a fulcrum that is at the
end of the lever.
Second-class levers are force
multipliers.
The load is always between
the effort and the fulcrum.
Examples include:
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bottle opener
springboard
wheelbarrow
wrench
nutcracker
oar - the water is the fulcrum;
the boat is the load and the
effort is at the inboard end
Second-class levers in your body
Stand on tip toes
 The pivot is at your toe joints and
your foot acts as a lever arm.
 Your calf muscles and Achilles
tendon provide the effort when
the calf muscle contracts. The
load is your body weight and is
lifted by the effort.
 The effort force needed is less
than the load force, so there is a
mechanical advantage.
 This muscular movement at the
back of your legs allows you to
move your whole body a small
distance.
Third-Class Levers
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Third-class levers are those in
which the effort is between
the fulcrum and the load.
Third-class levers are speed
multipliers.
Examples include:
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tennis racquet
tongs
hammer
broom
fishing rod
spring-loaded mousetrap
leg when kicking football
Third-class levers in your body
Bend your arm
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The pivot is at the elbow and the
forearm acts as the lever arm.
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The biceps muscle provides the effort
(force) and bends the forearm against
the weight of the forearm and any
weight that the hand might be holding.
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There is no mechanical advantage
because the effort is greater than the
load. However this disadvantage is
compensated with a larger movement
– a small contraction of the biceps
produces a large movement of the
forearm.
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This type of lever system also gives us
the advantage of a much greater
speed of movement.
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Many muscle and bone combinations in
our bodies are of the Class 3 lever
type.
Mechanical Advantage
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Mechanical advantage
measures how much easier a
lever makes a task.
Mechanical advantage
= load
effort
For a first class lever, placing
the fulcrum closer to the load
means that less effort can be
exerted to move a heavier
load. This means the lever
will have a greater
mechanical advantage.
Levers in Everyday Life –Goldfields
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Windlasses used a wheel and
axle (first class lever) to wind
buckets of rock and soil to top
of the mining shaft. The miner
at the top turned the handle
(the wheel) and the rope
wound around the axle,
raising the bucket.
Whips were simple first-class
levers used to lift buckets of
rock and soil to the top the
mining shaft. Longer handles
made lifting easier.
Levers in Everyday Life – Building Sites
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Hammer removing nail
is a first-class lever
Wheel-barrow
handles are a secondclass levers
Screwdrivers are
simple wheel and
axles (first-class lever)
Levers in Everyday Life - Kitchen
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Using a spoon to open
milo can is using it as a
first-class lever
Wheel and axle
combinations include
taps (force multiplier)
and ceiling fans (speed
multipliers)
Hinges on cupboards
are second-class levers
Levers in Everyday Life - Sport
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Tennis racquets, cricket bats
and softball bats are all
third-class levers - they
make objects move faster
and further.
Rowing – the oar acts as a
second class lever.
Diving – the springboard
acts as a second class lever.

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